Ink formulations and film constructions thereof

ABSTRACT

Ink formulations suitable for deposition upon the intermediate transfer member of an indirect printing system and for transfer therefrom to a substrate. The inks are aqueous inkjet inks comprising an organic polymeric resin and a colorant. Ink film constructions including a plurality of continuous ink films fixedly adhered to the printing substrate that can be obtained with these inks are also disclosed. The inks and the printed constructions are such that the ink films and the dried inks composing them have a first dynamic viscosity within a range of 10 6  cP to 5·10 7  cP at at least a first temperature within a first range of 60° C. to 87.5° C., and a second dynamic viscosity of at least 6·10 7  cP, for at least a second temperature within a second range of 50° C. to 55° C.

RELATED APPLICATION INFORMATION

The present application is a continuation of U.S. patent applicationSer. No. 16/048,299 which was filed on Jul. 29, 2018 and is incorporatedherein by reference in its entirety. U.S. patent application Ser. No.16/048,299 is a continuation of U.S. patent application Ser. No.14/917,461, which is a 371 national stage entry of PCT/IB2014/002395filed on Sep. 11, 2014, which claims the benefit of U.S. provisionalapplication No. 61/876,727 filed on Sep. 11, 2013 and claims priorityfrom GB 1401173.8 filed on Jan. 23, 2014. The contents of the aforesaidapplications are incorporated herein by reference as if fully set forthherein.

FIELD AND BACKGROUND OF THE DISCLOSURE

The present invention relates to ink formulations suitable for ink jetprinting systems, and more particularly for indirect printing systems.Ink film constructions produced using such inks including ink dots, andmore particularly continuous ink dots, adhered to printing substratesare also disclosed.

Currently, lithographic printing is the process in most common use forproducing newspapers and magazines. Lithographic printing involves thepreparation of plates bearing the image to be printed, which plates aremounted on a plate cylinder. An ink image produced on the plate cylinderis transferred to an offset cylinder that carries a rubber blanket. Fromthe blanket, the image is applied to paper, card or another printingmedium, termed the substrate, which is fed between the offset cylinderand an impression cylinder. For a wide variety of well-known reasons,offset litho printing is suitable, and economically viable, only forlong print runs.

More recently, digital printing techniques have been developed thatallow a printing device to receive instructions directly from a computerwithout the need to prepare printing plates. Amongst these are colorlaser printers that use the xerographic process. Color laser printersusing dry toners are suitable for certain applications, but they do notproduce images of a quality acceptable for publications such asmagazines.

A process that is better suited for short run high quality digitalprinting is used in the HP-Indigo digital printing press. In thisprocess, an electrostatic image is produced on an electrically chargedimage-bearing cylinder by exposure to laser light. The electrostaticcharge attracts oil-based inks to form a color ink image on theimage-bearing cylinder. The ink image is then transferred by way of ablanket cylinder onto the substrate. Though such systems are bettersuited for high quality digital printing, the use of oil-based inks hasraised environmental concerns.

Various printing devices have also previously been proposed that use anindirect inkjet printing process, this being a process in which aninkjet print head is used to print an image onto the surface anintermediate transfer member, which is then used to transfer the imageonto a substrate. The intermediate transfer member (also called an imagetransfer member or an ITM) may be a rigid drum or a flexible belt, alsoherein termed a blanket, guided over rollers.

Using an indirect printing technique overcomes many problems associatedwith inkjet printing directly onto the substrate. For example, inkjetprinting directly onto porous paper, or other fibrous material, resultsin poor image quality because of variation of the distance between theprint head and the surface of the substrate, and because of thesubstrate acting as a wick. Fibrous substrates, such as paper, generallyrequire specific coatings engineered to absorb the liquid ink in acontrolled fashion or to prevent its penetration below the surface ofthe substrate. Using specially coated substrates is, however, a costlyoption that is unsuitable for certain printing applications.Furthermore, the use of coated substrates creates its own problems inthat the surface of the substrate remains wet and additional costlysteps are needed to dry the ink so that it is not later smeared as thesubstrate is being handled, for example stacked or wound into a roll.Furthermore, excessive wetting of the substrate causes cockling andmakes printing on both sides of the substrate (also termed perfecting orduplex printing) difficult, if not impossible.

The use of an indirect technique, on the other hand, allows the distancebetween the image transfer surface and the inkjet print head to bemaintained constant, reduces wetting of the substrate as the ink can bedried on the image transfer surface (also termed the release layer)before being applied to the substrate. Consequently, the final imagequality of the ink film on the substrate is less affected by thephysical properties of the substrate.

Such complex indirect printing systems may operate under numerous setsof inter-related variables, including, among others, the formulation ofthe inks, the composition of the release layer interfacing therewith,the temperatures at which the inks are deposited, dried and transferred,and the pressure applied on the dried ink image to enable transfer.

While ink formulations have been proposed, and notwithstanding theirrespective quality in the printing systems they have been adapted to,there remains a need for further improvements in ink formulationssuitable for ink jetting, and in particular, ink formulations suitablefor ink jetting on the intermediate transfer member of an indirectprinting system. Quality ink film constructions are also desired.

SUMMARY OF THE INVENTION

According to some teachings of the present invention there is providedan ink product comprising (a) at least one colorant; and (b) at leastone organic polymeric resin; the ink product exhibiting, as asubstantially dry residue: (i) a dynamic viscosity being within a rangeof 10⁶ cP to 5·10⁷ cP over at least a part of a first temperature rangeof 60° C. to 87.5° C.; and (ii) the dynamic viscosity being at least6·10⁷ cP, over at least a part of a second temperature range of 50° C.to 55° C.

According to an aspect of the present invention there is provided an inkproduct comprising (a) at least one colorant; and (b) at least oneorganic polymeric resin; the ink product exhibiting, as a substantiallydry residue: (i) a dynamic viscosity being within a range of 10⁶ cP to5·10⁷ cP, 8·10⁷ cP, 1·10⁸ cP, 2·10⁸ cP, or 3·10⁸ cP, over at least apart of a first temperature range of 60° C. to 87.5° C., 60° C. to 100°C., 60° C. to 105° C., or 60° C. to 110° C.; and (ii) the dynamicviscosity being at least 6·10⁷ cP, over at least a part of a secondtemperature range of 50° C. to 55° C.

According to another aspect of the present invention there is providedan ink film construction comprising the ink product and a printingsubstrate; the ink product disposed as at least one substantially dryink film fixedly adhered to a surface of said printing substrate.

According to another aspect of the present invention, the ink product isan ink formulation comprising the ink product and a solvent containingwater, said at least one colorant dispersed or at least partly dissolvedwithin the solvent, said at least one organic polymeric resin dispersedwithin the solvent.

According to further features in the described preferred embodiments,the ink formulation is an aqueous inkjet ink, typically having at leastone of (i) a viscosity of 2 to 25 cP at at least one particulartemperature in a jetting temperature range of 20-60° C.; and (ii) asurface tension of at most 50 milliNewton/m at at least one particulartemperature within said jetting temperature range.

According to another aspect of the present invention there is provided awater-based inkjet ink formulation including: (a) a solvent containingwater; (b) at least one colorant dispersed or at least partly dissolvedwithin the solvent; and (c) at least one organic polymeric resin,dispersed within the solvent; the ink formulation forming, when dried, asubstantially dry ink residue having: (i) a dynamic viscosity within aviscosity range of 10⁶ cP to 5·10⁷ cP over at least part of a firsttemperature range of 60° C. to 87.5° C.; and (ii) a dynamic viscosity ofat least 6·10⁷ cP, over at least a part of a second temperature range of50° C. to 55° C.

According to another aspect of the present invention there is providedan ink film construction including: (a) a printing substrate; and (b) atleast one substantially dry ink film, fixedly adhered to a surface ofthe printing substrate, the ink film containing at least one colorantdispersed in an organic polymeric resin; a dynamic viscosity of the inkfilm being within a range of 10⁶ cP to 5·10⁷ cP over at least part of afirst temperature range of 60° C. to 87.5° C., and being at least 6·10⁷cP over at least a part of a second temperature range of 50° C. to 55°C.

According to another aspect of the present invention there is provided awater-based inkjet ink formulation including: (a) a solvent containingwater; (b) at least one colorant dispersed or at least partly dissolvedwithin the solvent; and (c) at least one organic polymeric resin,dispersed within the solvent; the ink formulation forming, when dried, asubstantially dry ink residue having: (i) a first dynamic viscositywithin a range of 10⁶ cP to 3·10⁸ cP over at least part of a firsttemperature range of 60° C. to 100° C., 60° C. to 105° C., or 60° C. to110° C.; and (ii) a second dynamic viscosity of at least 6·10⁷ cP, overat least a part of a second temperature range of 50° C. to 55° C.; thesecond dynamic viscosity at 55° C. exceeding the first dynamic viscosityat 85° C.; the ink formulation fulfilling at least one of the followingstructural properties: (A) at least one particular resin of the organicpolymeric resin has an elevated glass transition temperature (T_(g)) ofat least 52° C., at least 54° C., at least 56° C., at least 58° C., atleast 60° C., at least 65° C., at least 70° C., at least 75° C., atleast 80° C., at least 85° C., at least 90° C., or at least 95° C.; (B)the substantially dry ink residue has, at at least one of 100° C., 90°C., 85° C., 80° C., 75° C., and 70° C., an overall transferabilityrating of at least 0.90; (C) the at least one particular resin has aminimum film-forming temperature (MFFT) of at least 48° C., at least 50°C., at least 52° C., at least 54° C., at least 56° C., at least 58° C.,at least 60° C., at least 65° C., at least 70° C., or at least 75° C.;(D) the formulation includes a softening agent having a vapor pressureof at most 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20kPa, at most 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08kPa, at most 0.06 kPa, or at most 0.05 kPa, at 150° C.; and (E) theformulation includes a softening agent selected to reduce said elevatedglass transition temperature by at least 5° C., at least 7° C., at least10° C., at least 15° C., at least 20° C., at least 25° C., at least 30°C., at least 40° C., or at least 50° C.

According to another aspect of the present invention there is providedan ink film construction including: (a) a printing substrate; and (b) atleast one substantially dry ink film, fixedly adhered to a surface ofthe printing substrate, the ink film containing at least one colorantdispersed in an organic polymeric resin; the ink film fulfilling atleast one of the following structural properties: (A) at least oneparticular resin of the organic polymeric resin has an elevated glasstransition temperature (T_(g)) of at least 52° C., at least 54° C., atleast 56° C., at least 58° C., at least 60° C., at least 65° C., atleast 70° C., at least 75° C., at least 80° C., at least 85° C., atleast 90° C., or at least 95° C.; (B) the substantially dry ink residuehas, at at least one of 100° C., 90° C., 85° C., 80° C., 75° C., and 70°C., a transferability rating of at least 0.90; (C) the at least oneparticular resin has a minimum film-forming temperature (MFFT) of atleast 48° C., at least 50° C., at least 52° C., at least 54° C., atleast 56° C., at least 58° C., at least 60° C., at least 65° C., atleast 70° C., or at least 75° C.; (D) the formulation includes asoftening agent having a vapor pressure of at most 0.40 kPa, at most0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0.15 kPa, at most0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or atmost 0.05 kPa, at 150° C.; and (E) the formulation includes a softeningagent selected to reduce said elevated glass transition temperature byat least 5° C., at least 7° C., at least 10° C., at least 15° C., atleast 20° C., at least 25° C., at least 30° C., at least 40° C., or atleast 50° C.; the ink film exhibiting at least one of the followingstructural properties: (I) a first dynamic viscosity within a range of10⁶ cP to 3·10⁸ cP over at least part of a first temperature range of60° C. to 100° C., 60° C. to 105° C., or 60° C. to 110° C.; and a seconddynamic viscosity of at least 6·10⁷ cP, over at least a part of a secondtemperature range of 50° C. to 55° C., the second dynamic viscosity at55° C. exceeding the first dynamic viscosity at 85° C.; (II) the inkfilm includes a single ink dot covering an area of the surface; the inkdot fulfilling a structural condition wherein, with respect to adirection normal to the surface over all of the area, the single ink dotis disposed entirely above the area; an average or characteristicthickness of the single ink dot being at most 1,800 nm; (III) the inkfilm includes an ink dot set or field contained within a squaregeometric projection projecting on the printing substrate, the ink dotset containing at least 10 distinct ink dots, fixedly adhered to asurface of the printing substrate, all the ink dots within the squaregeometric projection being counted as individual members of the set,each of the dots having an average thickness of less than 2,000 nm, anda diameter of 5 to 300 micrometers; each of the ink dots having agenerally convex shape in which a deviation from convexity, (DC_(dot)),is defined by:

DC _(dot)=1−AA/CSA,

AA being a calculated projected area of the dot, the area disposedgenerally parallel to the first fibrous printing substrate; and CSAbeing a surface area of a convex shape that minimally bounds a contourof the projected area; a mean deviation from convexity (DC_(dot mean))of the ink dot set being at most 0.085; and (IV) the above-described inkdot set, each of the dots having an average thickness of less than 2,000nm, and a diameter of 5 to 300 micrometers; each of the ink dots havinga deviation from a smooth circular shape, (DR_(dot)), represented by:

DR _(dot)=[P ²/(4π·A)]−1,

P being a measured or calculated perimeter of the ink dot; A being amaximal measured or calculated area contained by the perimeter; a meandeviation (DR_(dot mean)) of the ink dot set being at most 0.85.

According to further features in the described preferred embodiments,the dynamic viscosity within the first temperature range is at most2·10⁸ cP, 1·10⁸ cP, or 8·10⁷ cP.

According to still further features in the described preferredembodiments, the ratio of the second dynamic viscosity, at 55° C., tothe first dynamic viscosity, at 85° C., is at least 1.7, at least 2, atleast 2.5, at least 3, at least 4, at least 4.5, at least 5, at least 6,at least 7, at least 8, or at least 10.

According to still further features in the described preferredembodiments, this viscosity ratio is at most 30, at most 25, at most 20,at most 15, or at most 12.

According to still further features in the described preferredembodiments, the colorant includes at least one pigment.

According to still further features in the described preferredembodiments, the total concentration of the colorant and the resinwithin the ink dot is at least 7%, at least 10%, at least 15%, at least20%, at least 30%, at least 40%, at least 50%, at least 60%, at least70%, or at least 85%.

According to still further features in the described preferredembodiments, the weight ratio of the resin to the colorant within theplurality of ink films is at least 1:1, at least 1.25:1, at least 1.5:1,at least 1.75:1, at least 2:1, at least 2.5:1, at least 3:1, at least3.5:1, at least 4:1, at least 5:1, at least 7:1, or at least 10:1.

According to still further features in the described preferredembodiments, the ink dot contains less than 2%, less than 1%, less than0.5%, or less than 0.1% of one or more charge directors, or issubstantially devoid of charge directors.

According to still further features in the described preferredembodiments, the ink films contain at most 5%, at most 3%, at most 2%,at most 1%, or at most 0.5% inorganic filler particles (such as silicaor titania), by weight.

According to still further features in the described preferredembodiments, the formulation contains at most 20%, at most 16%, at most13%, at most 10%, at most 8%, at most 6%, at most 4%, at most 3%, atmost 2%, at most 1%, or at most 0.2% glycerol, by weight.

According to still further features in the described preferredembodiments, the ink dot contains less than 5%, less than 3%, less than2%, or less than 0.5% of one or more hydrocarbons or oils, or issubstantially devoid of such hydrocarbons or oils.

According to still further features in the described preferredembodiments, the ink films are disposed as laminates onto the surface ofthe printing substrate.

According to still further features in the described preferredembodiments, fibers of the fibrous printing substrate directly contactthe ink dot.

According to still further features in the described preferredembodiments, the commodity coated fibrous printing substrate contains acoating having less than 10%, less than 5%, less than 3%, or less than1%, by weight, of a water-absorbent polymer.

According to still further features in the described preferredembodiments, the fibrous printing substrate is a paper, optionallyselected from the group of papers consisting of bond paper, uncoatedoffset paper, coated offset paper, copy paper, groundwood paper, coatedgroundwood paper, freesheet paper, coated freesheet paper, and laserpaper.

According to still further features in the described preferredembodiments, the average (total) thickness of the ink film is within arange of 100-1,200 nm, 200-1,200 nm, 200-1,000 nm, 100-800 nm, 100-600nm, 100-500 nm, 100-450 nm, 100-400 nm, 100-350 nm, 100-300 nm, 200-450nm, 200-400 nm, or 200-350 nm.

According to still further features in the described preferredembodiments, the average (total) ink film thickness or single ink-dotthickness is at least 150 nm, at least 200 nm, at least 250 nm, at least300 nm, or at least 350 nm.

According to still further features in the described preferredembodiments, the average single ink-dot thickness is within a range of100-800 nm, 100-600 nm, 100-500 nm, 100-450 nm, 100-400 nm, 100-350 nm,100-300 nm, 200-450 nm, 200-400 nm, or 200-350 nm.

According to still further features in the described preferredembodiments, the ink film has an average thickness or height of at most5,000 nm, at most 4,000 nm, at most 3,500 nm, at most 3,000 nm, at most2,500 nm, or at most 2,000 nm.

According to still further features in the described preferredembodiments, the ink film has an average thickness or height of at most1,800 nm, at most 1,500 nm, at most 1,200 nm, at most 1,000 nm, at most800 nm, at most 650 nm, at most 500 nm, at most 450 nm, or at most 400nm.

According to still further features in the described preferredembodiments, the square geometric projection has a side length within arange of 0.5 mm to 15 mm, or about 10 mm, 5 mm, 2 mm, 1 mm, 0.8 mm, or0.6 mm.

According to still further features in the described preferredembodiments, the diameter of the inkjet dot is at least 7, at least 10,at least 12, at least 15, at least 18, or at least 20 micrometers.

According to further features in the described preferred embodiments,the first dynamic viscosity is at most 4·10⁷ cP, at most 3·10⁷ cP, atmost 2.5·10⁷ cP, at most 2·10⁷ cP, at most 1.5·10⁷ cP, or at most 1·10⁷cP.

According to still further features in the described preferredembodiments, the first dynamic viscosity is at least 2·10⁶ cP, at least4·10⁶ cP, at least 6·10⁶ cP, at least 7·10⁶ cP, at least 8·10⁶ cP, or atleast 9·10⁶ cP.

According to still further features in the described preferredembodiments, the first dynamic viscosity is within a range of 10⁶ cP to4·10⁷ cP, 10⁶ cP to 3·10⁷ cP, 10⁶ cP to 2·10⁷ cP, 3·10⁶ cP to 4·10⁷ cP,3·10⁶ cP to 3·10⁷ cP, 5·10⁶ cP to 3·10⁷ cP, 7·10⁶ cP to 3·10⁷ cP, 8·10⁶cP to 3·10⁷ cP, 9·10⁶ cP to 3·10⁷ cP, 10⁷ cP to 5·10⁷ cP, 10⁷ cP to5·10⁷ cP, 10⁷ cP to 4·10⁷ cP, 10⁷ cP to 3·10⁷ cP, 1.5·10⁷ cP to 3·10⁷cP, or 10⁷ cP to 3·10⁷ cP.

According to still further features in the described preferredembodiments, the second dynamic viscosity within the second temperaturerange is at least 8·10⁷ cP, at least 9·10⁷ cP, at least 10⁸ cP, at least1.2·10⁸ cP, at least 1.5·10⁸ cP, at least 2.0·10⁸ cP, at least 2.5·10⁸cP, at least 3.0·10⁸ cP, at least 3.5·10⁸ cP, at least 4.0·10⁸ cP, atleast 5.0·10⁸ cP, or at least 7.5·10⁸ cP.

According to still further features in the described preferredembodiments, this second dynamic viscosity is at most 6·10⁹ cP, at most4·10⁹ cP, at most 3·10⁹ cP, at most 2·10⁹ cP, at most 1.5·10⁹ cP, or atmost 10⁹ cP.

According to still further features in the described preferredembodiments, this second dynamic viscosity is within a range of 7·10⁷ cPto 5·10⁹ cP, 7·10⁷ cP to 3·10⁹ cP, 7·10⁷ cP to 2·10⁹ cP, 7·10⁷ cP to1·10⁹ cP, 8·10⁷ cP to 5·10⁹ cP, 9·10⁷ cP to 5·10⁹ cP, 9·10⁷ cP to 3·10⁹cP, 9·10⁷ cP to 2·10⁹ cP, 9·10⁷ cP to 1.5·10⁹ cP, 1·10⁸ cP to 5·10⁹ cP,1·10⁸ cP to 3·10⁹ cP, 1·10⁸ cP to 2·10⁹ cP, or 1.5·10⁸ cP to 1.5·10⁹ cP.

According to still further features in the described preferredembodiments, the upper temperature limit of the first temperature rangeis 87° C., 86° C., 85° C., 84° C., 82° C., 80° C., 78° C., 76° C., 74°C., 72° C., 70° C., or 68° C.

According to still further features in the described preferredembodiments, the lower temperature limit of this range is 61° C., 62°C., 63° C., 64° C., or 65° C.

According to still further features in the described preferredembodiments, the ink films or dried ink residue have a glass transitiontemperature (T_(g)) of at least 52° C., at least 54° C., at least 56°C., at least 58° C., at least 60° C., at least 65° C., at least 70° C.,at least 75° C., at least 80° C., at least 85° C., at least 90° C., orat least 95° C.

According to still further features in the described preferredembodiments, the plurality of ink films or dried ink residue contain atleast one water-soluble material or at least one water-dispersiblematerial, optionally including an aqueous dispersant.

According to still further features in the described preferredembodiments, the ink films or dried ink residue contain at least 2%, atleast 3%, at least 5%, or at least 8%, by weight, of the water-solublematerial.

According to still further features in the described preferredembodiments, the ink films or dried ink residue contain at least 1.2%,at least 1.5%, at least 2%, at least 3%, at least 4%, at least 6%, atleast 8%, at least 10%, at least 12%, at least 15%, or at least 20% ofthe colorant, by weight.

According to still further features in the described preferredembodiments, the ink films or dried ink residue contain at least 20%, atleast 30%, at least 40%, at least 50%, at least 60%, or at least 70% ofthe resin, by weight.

According to still further features in the described preferredembodiments, ΔT defines a temperature differential between a temperature(T_(F)) at which the ink films or dried ink residue begin to exhibit aparticular degree of flowability, and a baseline temperature (T_(B)):

ΔT=T _(F) −T _(B)

the degree of flowability being defined by a critical viscosity (μ_(CR))at which the degree of flowability is achieved, and wherein, when thebaseline temperature equals 50° C., and the critical viscosity equals10⁸ cP, the temperature differential is at least 3° C., at least 4° C.,at least 5° C., at least 7° C., at least 12° C., at least 15° C., atleast 18° C., at least 20° C., or at least 25° C.

According to still further features in the described preferredembodiments, the printing substrate is a fibrous printing substrate, acommodity coated printing substrate, an uncoated printing substrate, ora coated or uncoated offset substrate.

According to still further features in the described preferredembodiments, the continuous ink film of the continuous ink films isdefined as an ink dot, a dimensionless aspect ratio (R_(aspect)) isdefined by:

R _(aspect) =D _(dot) /H _(dot)

wherein: D_(dot) is an average diameter of the dot; H_(dot) is anaverage thickness of the dot; the dimensionless aspect ratio being atleast 15, at least 20, at least 25, or at least 30, at least 40, atleast 50, at least 60, at least 75, at least 85, at least 95, at least110, or at least 120.

According to still further features in the described preferredembodiments, the dimensionless aspect ratio is at most 200 or at most175.

According to still further features in the described preferredembodiments, the plurality of continuous ink films are fixedly adhereddirectly on the surface of the printing substrate.

According to still further features in the described preferredembodiments, the colorant constitutes at least 0.3%, at least 0.5%, atleast 0.7%, at least 0.85%, at least 1%, at least 1.2%, at least 1.4%,at least 1.6%, at least 1.8%, or at least 2%, by weight, of theformulation.

According to still further features in the described preferredembodiments, the formulation further includes a softening agentoptionally having a vapor pressure of at most 0.40 kPa, at most 0.35kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0.15 kPa, at most 0.12kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or at most0.05 kPa, at 150° C.

According to still further features in the described preferredembodiments, the softening agent is chemically stable up to atemperature of at least 170° C., at least 185° C., at least 200° C., orat least 220° C.

According to still further features in the described preferredembodiments, the formulation or the at least one organic polymeric resinfurther includes an aqueous dispersant, the dispersant optionallyconstituting at most 5%, at most 4.5%, at most 4%, at most 3.5 wt. %, atmost 3 wt. %, at most 2.5 wt. %, at most 2 wt. %, at most 1.5 wt. %, atmost 1 wt. % or at most 0.5 wt. % of the formulation.

According to still further features in the described preferredembodiments, the dispersant is selected from the group consisting ofhigh molecular weight polyurethanes or aminourethanes, styrene-acryliccopolymers, modified polyacrylate polymers, acrylic block copolymer madeby controlled free radical polymerization, sulfosuccinates, acetylenicdiols, ammonium salts of carboxylic acid, alkylol ammonium salts ofcarboxylic acid, aliphatic polyethers with acidic groups, andethoxylated non-ionic fatty alcohols.

According to still further features in the described preferredembodiments, the polymeric resin includes, or mainly includes, anacrylic-based polymer selected from the group consisting of an acrylicpolymer and an acrylic-styrene copolymer; or includes or mainly includeslinear or branched resins of polyester or co-polyester.

According to still further features in the described preferredembodiments, the ink formulation is formulated such that when diluted byat least 50%, at least 100%, at least 150%, at least 200%, at least250%, at least 300%, at least 350%, or at least 400%, on a weight/weightbasis by a diluting solvent or water, a resultant mixture is an aqueousinkjet ink having: (i) a viscosity of 2 to 25 cP at at least oneparticular temperature in a range of 20-60° C.; and (ii) a surfacetension of at most 50 milliNewton/m at at least one particulartemperature within the range.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is an exploded schematic perspective view of a printing system inaccordance with which an embodiment of the invention may be used;

FIG. 2 is a schematic vertical section through the printing system ofFIG. 1, in which the various components of the printing system are notdrawn to scale;

FIG. 3 is a schematic representation of a printing system of theinvention in accordance with which an embodiment of the invention may beused;

FIG. 4A provides temperature sweep plots of dynamic viscosity as afunction of temperature, for dried ink residues of various inkformulations, including ink formulations according to the presentinvention;

FIG. 4B provides temperature sweep plots of dynamic viscosity as afunction of temperature, for dried ink residues of inventive inkformulations containing various polyester resins;

FIG. 5 provides temperature sweep plots of dynamic viscosity as afunction of temperature, for representative dried ink dried residues ofvarious ink formulations provided in FIGS. 4A and 4B;

FIG. 6 provides temperature sweep plots of dynamic viscosity as afunction of temperature, for representative dried ink residues of inkformulations of the present invention, vs. dried ink residues of severalcommercially available inkjet inks;

FIG. 7A provides a first plurality of temperature sweep plots of dynamicviscosity as a function of temperature, for dried ink residues of fiveink formulations having identical components, and a varying ratio ofsoftening agent, using a first thermoplastic resin and a first softeningagent;

FIG. 7B provides a second plurality of temperature sweep plots ofdynamic viscosity as a function of temperature, for dried ink residuesof five ink formulations having identical components, and a varyingratio of softening agent, using a different thermoplastic resin and adifferent softening agent with respect to those used in FIG. 7A;

FIGS. 8A-8D are temperature sweep plots of dynamic viscosity as afunction of temperature, for residue films of ink formulations havingdifferent softening agents, and varying concentrations of those agents;

FIG. 9 provides temperature sweep plots of dynamic viscosity as afunction of temperature, for dried ink residues of four ink formulationshaving different colorants (C, M, Y, K) but otherwise identicalformulation components;

FIGS. 10A-F display two-dimensional (FIGS. 10A-C) and three-dimensional(FIGS. 10D-F) laser-microscope acquired magnified images of ink films oncoated paper substrates, obtained using various printing technologies,wherein: FIGS. 10A and 10D are magnified images of a liquidelectro-photography film (LEP); FIGS. 10B and 10E are magnified imagesof an offset splotch; and FIGS. 10C and 10F are magnified images of aninkjet ink film construction according to the present invention;

FIGS. 11A-F display two-dimensional (FIGS. 11A-C) and three-dimensional(FIGS. 11D-F) laser-microscope acquired magnified images of ink films onuncoated paper substrates, obtained using various printing technologies,wherein: FIGS. 11A and 11D are magnified images of a liquidelectro-photography film (LEP); FIGS. 11B and 11E are magnified imagesof an offset splotch; and FIGS. 11C and 11F are magnified images of aninkjet ink film construction according to the present invention;

FIGS. 12A-1, 12B-1, 12C-1, 12D-1 and 12E-1 provide magnified views ofrespective fields of ink dots or films on respective samples ofcommodity-coated fibrous substrates (FIGS. 12A-1, 12B-1 and 12C-1) anduncoated fibrous substrates (FIGS. 12D-1 and 12E-1), each of the fieldsof ink dots or films being produced using an ink formulation of thepresent invention, and each of the five figures relating to a differentfibrous substrate;

FIGS. 12A-2, 12B-2, 12C-2, 12D-2 and 12E-2 provide a further magnifiedview of a portion of each of the corresponding frames of FIGS. 12A-1,12B-1, 12C-1, 12D-1 and 12E-1, respectively;

FIGS. 12A-3, 12B-3, 12C-3, 12D-3 and 12D-E provide corresponding opticaluniformity profiles for each of the respective samples of FIGS. 12A-2,12B-2, 12C-2, 12D-2 and 12E-2;

FIGS. 12A-4, 12B-4, 12C-4, 12D-4 and 12E-4 provide correspondingimage-processor computed contours and convexity projections for each ofthe respective samples of FIGS. 12A-2, 12B-2, 12C-2, 12D-2 and 12E-1;

FIG. 13A provides a magnified view of a field of ink dots on acommodity-coated fibrous substrate, produced using a commerciallyavailable, aqueous, direct inkjet printer;

FIG. 13B provides a magnified view of a field of ink dots on an uncoatedfibrous substrate, produced using the identical, commercially available,aqueous, direct inkjet printer;

FIGS. 14A-1, 14B-1, 14C-1, 14D-1, 14E-1 and 14F-1 provide opticaluniformity profiles of respective images of ink splotches or filmsobtained using various prior-art printing technologies on uncoated(FIGS. 14A-1, 14B-1 and 14C-1) and coated (FIGS. 14D-1, 14E-1 and 14F-1)paper; corresponding FIGS. 14A-2, 14B-2, 14C-2, 14D-2, 14E-2 and 14F-2show said respective images.

FIGS. 14A-3, 14B-3, 14C-3, 14D-3, 14E-3 and 14F-3 provide correspondinganalyses of the ink splotches or films provided in FIGS. 14A-1, 14B-1,14C-1, 14D-1, 14E-1 and 14F-1, respectively;

FIG. 15A shows a two-dimensional shape having the mathematical propertyof a convex set;

FIG. 15B shows a two-dimensional shape having the mathematical propertyof a non-convex set;

FIG. 15C is a schematic top projection of an ink film having a rivuletand an inlet, the schematic projection showing a smoothed projection ofthe ink image;

FIGS. 16A and 16B provide respective schematic cross-sectional views ofan inventive ink film construction and an inkjet ink dot construction ofthe prior art, wherein the substrate is a fibrous paper substrate; and

FIGS. 17A and 17C each show an image of the surface of the outer layerof an intermediate transfer member; FIGS. 17B and 17D are correspondingimages of the surface of the ink films produced using those outerlayers, in accordance with the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The ink formulations and ink film constructions according to the presentinvention may be better understood with reference to the drawings andthe accompanying description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

The inventive ink formulations may be used, and the ink filmconstructions may be obtained, in particular by the following printingprocess or by using any printing system implementing such process. Aprinting process suitable for use of the ink formulations hereindisclosed and for the preparation of the ink films according to theinvention includes directing droplets of an ink onto an intermediatetransfer member to form an ink image, the ink including an organicpolymeric resin and a colorant (e.g., a pigment or dye) in an aqueouscarrier, and the transfer member having a hydrophobic outer surface,each ink droplet in the ink image spreading on impinging upon theintermediate transfer member to form a wet ink film (e.g., a thin filmpreserving a major part of the flattening and horizontal extension ofthe droplet present on impact or covering an area dependent upon themass of ink in the droplet). The ink is dried while the ink image isbeing transported by the intermediate transfer member by evaporating theaqueous carrier from the ink image to leave a dry or substantially dryresidue film including resin and colorant. The residue film is thentransferred to a substrate (e.g., by pressing the intermediate transfermember against the substrate to impress the residue film thereupon). Thechemical compositions of the ink and of the surface of the intermediatetransfer member are selected such that attractive intermolecular forcesbetween molecules in the outer skin of each droplet and on the surfaceof the intermediate transfer member counteract the tendency of the inkfilm produced by each droplet to bead under the action of the surfacetension of the aqueous carrier, without causing each droplet to spreadby wetting the surface of the intermediate transfer member. Furtherdetails on such printing process and exemplary printing systems suitablefor use with the ink formulations of the present invention and enablingthe ink film constructions thereof are disclosed in PCT PublicationsNos. WO 2013/132418, WO 2013/132419 and WO 2013/132420.

The printing process sets out to preserve, or freeze, the thin pancakedisc shape of each aqueous ink droplet, that is caused by the flatteningof the ink droplet on impacting the surface of the intermediate transfermember (also termed the release layer), despite the low surface energyand hydrophobicity of this layer. To achieve this objective, this novelprocess relies on electrostatic interactions between molecules in theink and in the outer surface of the transfer member, the molecules beingeither charged in their respective medium or being mutually chargeable,becoming oppositely charged upon interaction between the ink and therelease layer. Further details on the printing process are providedhereinbelow.

General Overview of the Printing Process and System

The printing system shown in FIGS. 1 and 2 essentially includes threeseparate and mutually interacting systems, namely a blanket system 100,an image forming system 300 above the blanket system 100, and asubstrate transport system 500 below the blanket system 100. Whilecirculating in a loop, the blanket passes through various stations.Though the below description is provided in the context of theintermediate transfer member being an endless belt, the ink formulationsaccording to the invention are equally applicable to printing systemswherein the intermediate transfer member is a drum, the specific designsof the various stations being accordingly adapted.

The blanket system 100 includes an endless belt or blanket 102 that actsas an intermediate transfer member and is guided over two rollers 104,106. An image made up of dots of an aqueous ink is applied by imageforming system 300 to an upper run of blanket 102 at a location referredherein as the image forming station. A lower run selectively interactsat two impression stations with two impression cylinders 502 and 504 ofthe substrate transport system 500 to impress an image onto a substratecompressed between the blanket 102 and the respective impressioncylinder 502, 504. As will be explained below, the purpose of therebeing two impression cylinders 502, 504 is to permit duplex printing.Though not illustrated, duplex printing can also be achieved with asingle impression station using an adapted perfecting system able torefeed to the impression station on the reverse side a substrate alreadyprinted on its first side. In the case of a simplex printer, only oneimpression station would be needed.

In operation, ink images, each of which is a mirror image of an image tobe impressed on a final substrate, are printed by the image formingsystem 300 onto an upper run of blanket 102. In this context, the term“run” is used to mean a length or segment of the blanket between any twogiven rollers over which the blanket is guided. While being transportedby the blanket 102, the ink is heated to dry it by evaporation of most,if not all, of the liquid carrier. The ink image is furthermore heatedto render tacky the film of ink solids remaining after evaporation ofthe liquid carrier, this film being referred to as a residue film, todistinguish it from the liquid film formed by flattening of each inkdroplet. At the impression cylinders 502, 504 the image is impressedonto individual sheets 501 of a substrate which are conveyed by thesubstrate transport system 500 from an input stack 506 to an outputstack 508 via the impression cylinders 502, 504. Though not shown in thefigures, the substrate may be a continuous web, in which case the inputand output stacks may be replaced by a supply roller and a deliveryroller. The substrate transport system needs to be adapted accordingly,for instance by using guide rollers and dancers taking slacks of web toproperly align it with the impression station.

Image Forming System

The image forming system 300 includes print bars 302 which may each beslidably mounted on a frame positioned at a fixed height above thesurface of the blanket 102. Each print bar 302 may include a strip ofprint heads as wide as the printing area on the blanket 102 and includesindividually controllable print nozzles. The image forming system canhave any number of bars 302, each of which may contain an aqueous ink ofa different or of the same color, typically each jetting Cyan (C),Magenta (M), Yellow (Y) or Black (K) inks. It is possible for the printbars to deposit different shades of the same color (e.g., various shadesof gray, including black) or for two print bars or more to deposit thesame color (e.g., black). Additionally, the print bar can be used forpigmentless liquids (e.g., decorative or protective varnishes) and/orfor specialty colors (e.g., achieving visual effect, such as metallic,sparkling, glowing or glittering look, or even scented effect).

As some print bars may not be required during a particular printing job,the heads can be moved between an operative position (at which the barremains stationary), in which they overlie blanket 102 and aninoperative position (at which the bar can be accessed for maintenance).

Within each print bar, the ink may be constantly recirculated, filtered,degassed and maintained at a desired temperature and pressure, as knownto the person skilled in the art without the need for more detaileddescription.

As different print bars 302 are spaced from one another along the lengthof the blanket, it is of course essential for their operation to becorrectly synchronized with the movement of blanket 102.

If desired, it is possible to provide a blower following each print bar302 to blow a slow stream of a hot gas, preferably air, over theintermediate transfer member to commence the drying of the ink dropletsdeposited by the print bar 302. This assists in fixing the dropletsdeposited by each print bar 302, that is to say resisting theircontraction and preventing their movement on the intermediate transfermember, and also in preventing them from merging into droplets depositedsubsequently by other print bars 302. Such post jetting treatment of thejust deposited ink droplets, need not substantially dry them, but onlyenable the formation of a skin on their outer surface.

Blanket and Blanket Support System

The blanket 102, in one variation, is seamed. In particular, the blanketcan be formed of an initially flat strip of which the ends are fastenedto one another, releasably or permanently, to form a continuous loopoften referred to as a belt. A releasable fastening may be a zipfastener or a hook and loop fastener that lies substantially parallel tothe axes of rollers 104 and 106 over which the blanket is guided. Apermanent fastening may be achieved by the use of an adhesive or a tape.The continuous belt may be formed by more than one elongated blanketstrip and may therefore include more than one seam. Alternatively, thebelt may be seamless.

In order to avoid a sudden change in the tension of the blanket as theseam passes over rollers or other parts of the support system, it isdesirable to make the seam, as nearly as possible, of the same thicknessas the remainder of the blanket.

The primary purpose of the blanket is to receive an ink image from theimage forming system and to transfer that image dried but undisturbed tothe impression stations. To allow easy transfer of the ink image at eachimpression station, the blanket has a thin upper release layer that maybe highly hydrophobic. Under suitable conditions, a silanol-, sylyl- orsilane-modified or terminated polydialkylsiloxane silicone material andamino silicones have been found to work well in the composition of therelease layer. However the exact formulation of the silicone being curedis not critical as long as the selected material allows for release ofthe image from the transfer member to a final substrate.

The strength of the blanket can be derived from a support orreinforcement layer. In one instance, the reinforcement layer is formedof a fabric. If the fabric is woven, the warp and weft threads of thefabric may have a same or different composition or physical structure sothat the blanket may have, for reasons to be discussed below, greaterelasticity in its widthways direction (parallel to the axes of therollers 104 and 106) than in its lengthways direction.

The blanket may include additional layers between the reinforcementlayer and the release layer, for example to provide conformability andcompressibility of the release layer to the surface of the substrate.Other layers may be further included to act as a thermal reservoir or athermal barrier. An inner layer may further be provided to control thefrictional drag on the blanket as it is rotated over its supportstructure. Other layers may be included to adhere or connect theaforementioned layers one with another or to prevent migration ofmolecules therebetween.

The blanket support system may include thermally conductive supportplates 130 forming a continuous flat support surface both on the topside and the bottom side of the support frame. Electrical heatingelements can be inserted into transverse holes of the plates to applyheat to the plates 130 and through plates 130 to the blanket 102. Othermeans for heating the blanket will occur to the person of skill in theart and may include heating from below, above, or within the blanketitself.

Also mounted on the blanket support frame are two pressure or niprollers 140, 142, which can be raised and lowered from the lower run ofthe blanket. The pressure rollers are located on the underside of thesupport frame in gaps between the support plates 130 covering theunderside of the frame. The pressure rollers 140, 142 are alignedrespectively with the impression cylinders 502, 504 of the substratetransport system. Each impression roller and corresponding pressureroller, when both are engaged with the blanket passing therebetween,form an impression station.

In some instances, the blanket support system further includes acontinuous track that can engage formations on the side edges of theblanket to maintain the blanket taut in its width ways direction. Theformations may be spaced projections, such as the teeth of one half of azip fastener sewn or otherwise attached to the side edge of the blanket.Alternatively, the formations may be a continuous flexible bead ofgreater thickness than the blanket. The lateral formations may bedirectly attached to the edges of the blanket or through an intermediatestrip that can optionally provide suitable elasticity to engage theformations in their respective guiding track, while maintaining theblanket flat in particular at the image forming station. The lateraltrack guide channel may have any cross-section suitable to receive andretain the blanket lateral formations and maintain it taut. To reducefriction, the guide channel may have rolling bearing elements to retainthe projections or the beads within the channel. Further details onexemplary blanket lateral formations or seams that may be suitable forintermediate transfer members appropriate for use with the inkformulations of the present invention are disclosed in PCT PublicationNo. WO 2013/136220.

In order for the image to be properly formed on the blanket andtransferred to the final substrate and for the alignment of the frontand back images in duplex printing to be achieved, a number of differentelements of the system must be properly synchronized. In order toposition the images on the blanket properly, the position and speed ofthe blanket must be both known and controlled. For this purpose, theblanket can be marked at or near its edge with one or more markingsspaced in the direction of motion of the blanket. One or more sensors107 sense the timing of these markings as they pass the sensor. Thespeed of the blanket and the speed of the surface of the impressionrollers should be the same, for proper transfer of the images to thesubstrate from the transfer blanket. Signals from the sensor(s) 107 aresent to a controller 109 which also receives an indication of the speedof rotation and angular position of the impression rollers, for examplefrom encoders on the axis of one or both of the impression rollers (notshown). Sensor 107, or another sensor (not shown), also determines thetime at which the seam of the blanket passes the sensor. For maximumutility of the usable length of the blanket, it is desirable that theimages on the blanket start as close to the seam as feasible. Furtherdetails on exemplary control systems that may be suitable for printingsystems appropriate for use with the ink formulations of the presentinvention are disclosed in PCT Publication No. WO 2013/132424.

Blanket Pre-Treatment

FIG. 1 shows schematically a roller 190 positioned on the external sideof the blanket immediately before roller 106. Such a roller 190 may beused optionally to apply a thin film of pre-treatment solutioncontaining a conditioning chemical agent.

While a roller can be used to apply an even film, the pre-treatment orconditioning material can alternatively be sprayed onto the surface ofthe blanket and optionally spread more evenly, for example by theapplication of a jet from an air knife. Alternatively, the optionalconditioning solution may be applied by passing the blanket over a thinfilm of conditioning solution seeping through a cloth having no directcontact with the surface of the release layer. Independently of themethod used to apply the optional conditioning solution, if needed, thelocation at which such pre-print treatment can be performed may bereferred herein as the conditioning station. The alternative printingsystem illustrated in FIG. 3 may also include a conditioning station.

As noted, when the ink droplet impinges on the transfer member, themomentum in the droplet causes it to spread into a relatively flatvolume. In the prior art, this flattening of the droplet is almostimmediately counteracted by the combination of surface tension of thedroplet and the hydrophobic nature of the surface of the transfermember.

In some instances, the shape of the ink droplet is “frozen” such that atleast some and preferably a major part of the flattening and horizontalextension of the droplet present on impact is preserved. It should beunderstood that since the recovery of the droplet shape after impact isvery fast, the methods of the prior art would not effect phase change byagglomeration and/or coagulation and/or migration.

Without wishing to be bound by theory, it is believed that, on impact,the positive charges which have been placed on the surface of thetransfer member attract the negatively charged polymer resin particlesof the ink droplet that are immediately adjacent to the surface of themember. It is believed that, as the droplet spreads, this effect takesplace along a sufficient area of the interface between the spreaddroplet and the transfer member to retard or prevent the beading of thedroplet, at least on the time scale of the printing process, which isgenerally on the order of seconds.

As the amount of charge is too small to attract more than a small numberof charged resin particles in the ink, it is believed that theconcentration and distribution of the charged resin particles in thedrop is not substantially changed as a result of contact with thechemical agent on the release layer. Furthermore, since the ink isaqueous, the effects of the positive charge are very local, especiallyin the very short time span needed for freezing the shape of thedroplets.

Without wishing to be bound by theory, it is believed that in applying aconditioning agent or solution to the surface of the intermediatetransfer member, at least one type of positively-charged functionalgroup of the conditioning agent is adsorbed onto, or otherwise attachedto, the surface of the release layer. On the opposite side of therelease layer, facing the jetted ink drops, at least one type ofpositively-charged functional group of the conditioning agent isavailable and positioned to interact with the negatively charged speciesin the ink (e.g., in the resin).

Intermediate transfer members amenable to such treatment may include intheir release layer, by way of example, silanol-, sylyl- orsilane-modified or terminated polydialkyl-siloxane silicones, orcombinations thereof. Further details on exemplary release layers thatmay be suitable for use with the ink formulations of the presentinvention are disclosed in PCT Publication No. WO 2013/132432.

Chemical agents suitable for the preparation of such conditioningsolutions, if required, have relatively high charge density and can bepolymers containing amine nitrogen atoms in a plurality of functionalgroups, which need not be the same, and can be combined (e.g., primary,secondary, tertiary amines or quaternary ammonium salts). Thoughmacromolecules having a molecular weight from several hundred to severalthousand may be suitable conditioning agents, the inventors believe thatpolymers having a high molecular weight of 10,000 g/mole or more arepreferable. Suitable conditioning agents include cationic guar,guar-based polymers, cationic methacrylamide, methacrylamide-basedpolymers, and linear, branched or modified polyethylene imines (PEI).Further details on exemplary conditioning agents, and solutionstherefrom, that may be suitable in printing systems appropriate for usewith the ink formulations of the present invention are disclosed in PCTPublication No. WO 2013/132339.

The efficacy of this method and of the water-based treating solutionsassociated therewith, also termed “conditioning solutions”, wasestablished in laboratory experimental setups and in preliminary pilotprinting experiments. As disclosed in the above-mentioned applicationthe use of such solutions was highly beneficial, as assessed by theprint quality of the image following its transfer from the intermediatetransfer member to the printing substrate. The optical density of theprinted matter was considered of particular relevance and the use ofsuch method of blanket treatment prior to ink jetting clearly improvedthe measured outcome on the printing substrate.

According to the method originally developed by the Applicant, a verythin coating of conditioning solution was applied to the transfermember, immediately removed and evaporated, leaving no more than a fewmolecular layers of the suitable chemical agent. Ink droplets werejetted on such pre-treated blanket, dried and transferred to theprinting substrate. Typically, the ink film image so printed could beidentified by the presence on their outer surface of the conditioningagent. In other words, the dried ink droplet upon transfer peeled awaythe underlayer of conditioning agent, which was then impressed on thefinal substrate in inversed orientation.

Exemplary conditioning solutions include Conditioning Solution A,provided below, and its plain counterpart, in which the conditioningagent is diluted in distilled water (1:99), without additives.

Conditioning Solution A PEI Lupasol ® PS (BASF) 1 Sucrose 4 Water 95

Ink Image Heating

The heaters, either inserted into the support plates 130 or positionedabove the blanket as intermediate drying system 224 and drying station214, are used to heat the blanket to a temperature that is appropriatefor the rapid evaporation of the ink carrier and compatible with thecomposition of the blanket. For blankets including, for instance,silanol-modified or terminated polydialkylsiloxane silicones in therelease layer, the temperature of heating may vary within a range from70° C. to 180° C., depending on various factors such as the compositionof the inks and/or of the conditioning solutions if needed. Blanketsincluding amino silicones may generally be heated to temperaturesbetween 70° C. and 130° C. Exemplary blankets comprising curedamino-functionalized silicones in their release layer are disclosed inPCT Publication No. WO 2013/132438.

In some printing systems, the temperature of the blanket may remainrelatively similar along the loop followed by the blanket, with optionallocalized transient change in temperature (e.g., to facilitate transferof the dried ink image from the transfer member to the printingsubstrate). In other printing systems, the temperature of the blanketmay vary as desired among the stations it passes. For example, the inkformulations may be jetted at the image forming station upon a blanketat a relatively low temperature below the evaporation temperature of theink carrier (e.g., between 60° C. and 100° C., typically between 70° C.and 90° C.). The deposited ink droplets may thereafter be dried upon theblanket having then a higher temperature to facilitate the evaporationof the ink carrier (e.g., up to 200° C.). The blanket temperature may befurther modified so that its temperature is sufficient to enabletransfer of the dried ink image at the impression station. In hightemperature transfer processes, in which the blanket is further heatedat the nip of the impression station (e.g., via 231), the surfacetemperature could be transiently raised up to 170° C. In low temperaturetransfer processes, in which the blanket is not further heated followingink drying, the surface temperature at the impression station can bebelow 140° C., typically below 120° C. Following the impression station,the blanket temperature may be additionally changed to suit the optimaloperating condition of any station the printing system may include. Forexample, the blanket may be further heated or cooled to suit a coatingstation at which a varnish may be optionally applied on the printed inkimage. Finally, the blanket temperature may be further modified to allowit to re-enter the image forming station at a desired temperature. Forthis purpose, a printing system suitable for use with the inkformulations according to the invention may include a blanket coolingstation.

When using beneath heating of the transfer member, it may be desirablefor the blanket to have relatively high thermal capacity and low thermalconductivity, so that the temperature of the body of the blanket 102will not change significantly as it moves between the optionalpre-treatment or conditioning station, the image forming station and theimpression station(s). When using top heating of the transfer member,the blanket would preferably include a thermally insulating layer toprevent undue dissipation of the applied heat. To apply heat atdifferent rates to the ink image carried by the transfer surface,independently of the architecture of a particular printing system,additional external heaters or energy sources (not shown) may be used toapply energy locally, for example prior to reaching the impressionstations to render the ink residue tacky (see 231 in FIG. 3), prior tothe image forming station to dry the conditioning agent if necessary andat the ink jetting station to start evaporating the carrier from the inkdroplets as soon as possible after they impact the surface of theblanket. Conversely, the printing system may include cooling stations tolocally remove excess heat.

The external heaters may be, for example, hot gas or air blowers 306 (asrepresented schematically in FIG. 1) or radiant heaters focusing, forexample, infrared radiation onto the surface of the blanket, which mayattain temperatures in excess of 50° C., 75° C., 100° C., 125° C., 150°C., 175° C., 190° C., 200° C., 210° C., or even 220° C.

After evaporating the aqueous carrier, including any liquid humectant,from the ink image, a dry or substantially dry residue film includingresin and colorant is obtained. The dried residue film left behind mayhave an average single drop ink film thickness below 1,500 nm (nm),below 1,200 nm, below 1,000 nm, below 800 nm, below 600 nm, below 500nm, below 400 nm, or below 300 nm.

For multiple drop ink films, the average thickness may be below 2,500nm, below 2,000 nm, below 1,600 nm, below 1,400 nm, below 1,200 nm,below 1,000 nm, below 800 nm, or below 600 nm.

As explained above, temperature control is of paramount importance tothe printing system if printed images of high quality are to beachieved. This is considerably simplified in the embodiment of FIG. 3 inthat the thermal capacity of the belt is much lower than that of theblanket 102 in the embodiments of FIGS. 1 and 2. The exemplary printingsystem schematically illustrated in FIG. 3 has an endless belt 210 thatcycles through an image forming station 212, a drying station 214, andan impression station 216, each of these stations acting as previouslydescribed. For instance, the image forming station 212 of FIG. 3 issimilar to the previously described image forming system 300,illustrated for example in FIG. 1. Following each print bar 222 in theimage forming station, an intermediate drying system 224 is provided toblow hot gas (usually air) onto the surface of the belt 210 to dry theink droplets partially. This hot gas flow assists in preventing blockageof the inkjet nozzles and also prevents the droplets of different colorinks on the belt 210 from merging into one another. In the dryingstation 214, the ink droplets on the belt 210 are exposed to radiationand/or hot gas in order to dry the ink more thoroughly, driving offmost, if not all, of the liquid carrier and leaving behind only a layerof resin and coloring agent which is heated to the point of beingrendered tacky.

In the impression station 216, the belt 210 passes between an impressioncylinder 220 and a pressure cylinder 218 that carries a compressibleblanket 219. The length of the blanket 219 is equal to or greater thanthe maximum length of a sheet 226 of substrate on which printing is totake place. The impression cylinder 220 has twice the diameter of thepressure cylinder 218 and can support two sheets 226 of substrate at thesame time. Sheets 226 of substrate are carried by a suitable transportmechanism (not shown in FIG. 3) from a supply stack 228 and passedthrough the nip between the impression cylinder 220 and the pressurecylinder 218. Within the nip, the surface of the belt 220 carrying theink image is pressed firmly by the blanket 219 of the pressure cylinder218 against the substrate so that the ink image is impressed onto thesubstrate and separated neatly from the surface of the belt. Thesubstrate is then transported to an output stack 230.

In some printing systems, a heater 231 may be provided shortly prior tothe nip between the two cylinders 218 and 220 of the image impressionstation to assist in rendering the ink film tacky, so as to facilitatetransfer to the substrate.

In order for the ink to separate neatly from the surface of the belt 210it is necessary for the latter surface to have a hydrophobic releaselayer. In the embodiment of FIG. 1, this hydrophobic release layer isformed as part of a thick blanket that also includes a compressibleconformability layer which is necessary to ensure proper contact betweenthe release layer and the substrate at the impression station. Theresulting blanket is a very heavy and costly item that needs to bereplaced in the event a failure of any of the many functions that itfulfills.

In the embodiment of FIG. 3, the hydrophobic release layer forms part ofa separate element from the thick blanket 219 that is needed to press itagainst the substrate sheets 226. In FIG. 3, the release layer is formedon the flexible thin inextensible belt 210 that is preferably fiberreinforced for increased tensile strength in its lengthwise dimension.

It will be appreciated that the description of a printing system asillustrated in FIG. 3 has been provided with a level of detailsufficient for those of ordinary skill in the art, to understand andcarry out the present invention.

It has also been proposed above in relation to the embodiment using athick blanket 102 to include additional layers affecting the thermalcapacity of the blanket in view of the blanket being heated frombeneath. The separation of the belt 210 from the blanket 219 in theembodiment of FIG. 3 allows the temperature of the ink droplets to bedried and heated to the softening temperature of the resin using muchless energy in the drying section 214. Furthermore, the belt may cooldown before it returns to the image forming station which reduces oravoids problems caused by trying to spray ink droplets on a hot surfacerunning very close to the inkjet nozzles. Alternatively andadditionally, a cooling station may be added to the printing system toreduce the temperature of the belt to a desired value before the beltenters the image forming station. Cooling may be effected by passing thebelt 210 over a roller of which the lower half is immersed in a coolant,which may be water or a cleaning/treatment solution, by spraying acoolant onto the belt of by passing the belt 210 over a coolantfountain.

For illustration, a conventional hydrophobic surface, such as a siliconecoated surface, will yield electrons readily and is regarded asnegatively charged. Polymeric resins in an aqueous carrier are likewisegenerally negatively charged. Therefore, in the absence of additionalsteps being taken the net intermolecular forces will cause theintermediate transfer member to repel the ink and the droplets will tendto bead into spherical globules.

In the novel printing process suitable for the preparation of ink filmconstructions according to the invention, the chemical composition ofthe surface of the intermediate transfer member is modified to provide apositive charge. This may be achieved, for example, by including in thesurface of the intermediate transfer member (e.g., embedded in therelease layer) molecules having one or more Brønsted base functionalgroups and in particular nitrogen including molecules. Suitablepositively charged or chargeable groups include primary amines,secondary amines, and tertiary amines Such groups can be covalentlybound to polymeric backbones and, for example, the outer surface of theintermediate transfer member may include amino silicones.

Such positively chargeable functional groups of the molecules of therelease layer may interact with Brønsted acid functional groups ofmolecules of the ink. Suitable negatively charged or chargeable groupsinclude carboxylated acids such as having carboxylic acid groups(—COOH), acrylic acid groups (—CH₂═CH—COOH), methacrylic acid groups(—CH₂═C(CH₃)—COOH) and sulfonates such as having sulfonic acid groups(—SO₃H). Such groups can be covalently bound to polymeric backbones andpreferably be water soluble or dispersible. Suitable ink molecules mayfor example include acrylic-based resins such as an acrylic polymer andan acrylic-styrene copolymer having carboxylic acid functional groups.

Inks

Inks in accordance with embodiments of the presently claimed invention,which are suitable for use in the process and in conjunction with thesystems described herein are, for example, aqueous inkjet inks thatcontain (i) a solvent including water and optionally a co-solvent, (ii)a negatively chargeable polymeric resin (the ink may include a smallamount of a pH-raising substance to ensure that the polymer isnegatively charged), and (iii) at least one colorant.

Prior to jetting, the ink typically has (i) a viscosity of 2 to 25centiPoise (cP) at at least one temperature in the range of 20-60° C.;and (ii) a surface tension of not more than 50 milliNewton/m at at leastone temperature in the range of 20-60° C. The colorant may contain apigment, preferably a nanopigment, for example having an averageparticle size (d₅₀) of not more than 120 nm.

In some embodiments, the polymeric resin includes primarily orexclusively one or more negatively chargeable polymers, such aspolyanionic polymers. By a “negatively chargeable polymer” or“negatively chargeable polymer resin” is meant a polymer or polymericresin which has at least one proton which can easily be removed to yielda negative charge; as used herein, the term refers to an inherentproperty of the polymer, and thus may encompass polymers which are in anenvironment in which such protons are removed, as well as polymers in anenvironment in which such protons are not removed.

In contrast, the term “a negatively charged polymer resin” refers to aresin in an environment in which one or more such protons have beenremoved.

Examples of negatively chargeable groups are carboxylic acid groups(—COOH), including acrylic acid groups (—CH₂═CH—COOH) and methacrylicacid groups (—CH₂═C(CH₃)—COOH), and sulfonic acid groups (—SO₃H). Suchgroups can be covalently bound to polymeric backbones; for examplestyrene-acrylic copolymer resins have carboxylic acid functional groupswhich readily lose protons to yield negatively-charged moieties. Manypolymers suitable for use in embodiments of the invention, whendissolved in water, will be negatively charged; others may require thepresence of a pH raising compound to be negatively charged. Commonly,polymers will have many such negatively chargeable groups on a singlepolymer molecule, and thus are referred to as polyanionic polymers.

Examples of polyanionic polymers include, for instance, polysulfonatessuch as polyvinylsulfonates, poly(styrenesulfonates) such as poly(sodiumstyrenesulfonate) (PSS), sulfonated poly(tetrafluoroethylene),polysulfates such as polyvinylsulfates, polycarboxylates such as acrylicacid polymers and salts thereof (e.g., ammonium, potassium, sodium,etc.), for instance, those available from BASF and DSM Resins,methacrylic acid polymers and salts thereof (e.g., EUDRAGIT®, amethacrylic acid and ethyl acrylate copolymer), carboxymethylcellulose,carboxymethylamylose and carboxylic acid derivatives of various otherpolymers, polyanionic peptides and proteins such as homopolymers andcopolymers of acidic amino acids such as glutamic acid, aspartic acid orcombinations thereof, homopolymers and copolymers of uronic acids suchas mannuronic acid, galacturonic acid and guluronic acid, and theirsalts, alginic acid and its salts, hyaluronic acid and its salts,gelatin, carrageenan, polyphosphates such as phosphoric acid derivativesof various polymers, polyphosphonates such as polyvinylphosphonates, aswell as copolymers, salts, derivatives, and combinations of thepreceding, among various others. In some embodiments, the polymericresin includes an acrylic-based polymer, viz. a polymer or copolymermade from acrylic acid or an acrylic acid derivative (e.g., methacrylicacid or an acrylic acid ester), such as polyacrylic acid or an acrylicacid-styrene copolymer. Nominally, the polymeric resin may be, orinclude, an acrylic styrene co-polymer. In some embodiments thepolymeric resin includes primarily or exclusively an acrylic-basedpolymer selected from an acrylic polymer and an acrylic-styrenecopolymer. In some instances, the polymeric resin is at least partlywater soluble; in some instances, the polymeric resin is waterdispersible, and may be provided as an emulsion or a colloid.

Numerous organic polymeric resins exist and many recognized to serve forthe preparation of ink compositions are commercially available and knownto persons skilled in this industry. Generally such polymers, whetherwell established ink resins or less typical to this field, serve toentrap (e.g., encapsulate) or otherwise immobilize or associate with thecoloring agent of relevance through physical, covalent or ionicinteractions, ultimately also enabling the ink image to attach to theprinted substrate. Such polymeric resins are therefore often referred toas binders. Some polymers may alternatively or additionally serve asdispersants, maintaining the ink formulations in desired suspension oremulsion form. Though the exact function of an organic polymeric resinmay vary in the context of a specific formulation or may include morethan one function, it is used herein to refer to the predominant binderfunction which typically account for most of such polymers presence in afinal ink composition.

Water dispersible thermoplastic resins include, but are not limited tolinear and branched acrylic polymers, acrylic styrene copolymers,styrene polymers, polyesters, co-polyesters, polyethers, polyamides orpolyester amides, polyurethanes and polyamines Such polymers aretypically supplied with basic data on their average molecular weight(MW), their glass transition (T_(g)) or softening temperature, theirminimal film forming temperature (MFFT), their hardness, their abilityto contribute to the gloss of the final printed inks, or to theiradherence to the printed substrate, or to their resistance to abrasion.Some polymers may be defined by their reactivity or by the density oftheir functional groups, the acid number or the hydroxyl number beingbut examples of such qualifications.

Ink formulators are familiar with such parameters and will readilyappreciate that the selection of a suitable organic polymeric resin maydepend on the intended purpose. For instance, binders need not providehigh gloss if the printed image is intended to be matte or if the inkimage is to be further laminated or coated with a varnish that wouldindependently provide the desired optical effect. Such gloss-relatedinformation is generally provided by the supplier, but can beindependently measured, for example, by using a gloss meter at a fixedangle of incidence. Using a Micro-gloss (BYK-Gardner, Germany)single-angle gloss meter at 75°, prints displaying a gloss above 65-70are regarded as glossy, whereas prints having a gloss below 65 areregarded as matte.

Similarly, the presence of a laminate or varnish may reduce the need toselect polymers providing good to excellent abrasion resistance. Eachsupplier may use variations of the standard resistance test ASTM D5264to assess this property. In absence of coating protection and if theprinted product is intended or may be subjected to scrub, then polymershaving higher abrasion resistance should be preferred. It can beappreciated that the hardness of the polymer can correlate with itsability to form ink film images that may have the desired resistance toabrasion, if needed. Therefore, for certain purposes, resins having agood to high hardness are preferred.

Such a coating may also improve the adhesion of the ink image to certainsubstrates. Understandingly, the degree of adherence a polymer wouldneed to have would depend on the intended substrate. Some organic resinsprovide good adherence to coated or synthetic substrates typicallyhaving a relatively low surface roughness. Other resins have superiorabilities and can additionally or alternatively adhere to substrateshaving a higher surface roughness, such as most of the uncoated printingsubstrates. The resins may also be selected to suit cellulose-based,cellulose-free, plastic-based or metal-based printing substrates, ascommonly used in the field of commercial printing. Advantageously,though not necessarily, a suitable organic polymeric resin shall beappropriate for a broad range of possible substrates. This capability toadhere to the substrate of choice, if not provided by the resinmanufacturer, can be readily assessed using a tape adherence test on theintended printing substrate.

The acid number, also termed the acid value or neutralization number,relates to the mass of potassium hydroxide (KOH) in milligrams that isrequired to neutralize one gram of a chemical substance. The acid numberis usually provided by the manufacturer, but readily measurable as perits definition. Resins having a high acid number are expected to yieldink films less stable when exposed to water (water fastness) and shouldtherefore be avoided when the intended use of the printed matter mayexpose it to conditions that would be deleterious to films comprisingsuch resins. Resins suitable for the present invention generally have anacid number below 220, below 180, below 150, below 120, below 100, orbelow 90. In some embodiments, the organic polymeric resins have an acidnumber between 20 and 220, between 60 and 100, and in particular,between 70 and 90.

In some embodiments, and in particular, for various embodimentsemploying a polyester or polyester-based resin, the acid number may bebelow 15, below 12, below 10, below 7, below 5, or below 2.5. Suchpolymeric resins may have an acid number between 0 and 15, between 0 and10, and in particular, between 0 and 5 or between 1 and 5.

The polymer resins, such as acrylic-based polymers, may be negativelycharged at alkaline pH. Consequently, in some embodiments, the polymericresin has a negative charge at a pH above 7.5, above 8 or above 9.Furthermore, the solubility or the dispersability of the polymeric resinin water may be affected by pH. Thus, in some embodiments, theformulation comprises a pH-raising compound. Examples of such arediethyl amine, monoethanol amine, and 2-amino-2-methyl propanol. SuchpH-raising compounds, when included in the ink, are generally includedin small amounts, e.g., about 1 wt. % of the formulation and usually notmore than about 2 wt. % of the formulation.

Some resins are characterized by a hydroxyl number, also termed thehydroxyl value, which is a measure of the content of free hydroxylgroups in a compound, hence typically used in connection with esters.This value, if not provided, can be determined by acetylation of thefree hydroxyl groups of the compound of interest and standard titrationsand calculations known in the art. As other functional groups, such asprimary or secondary amines, may take part in the chemical reactionsused to assess this number, they can also be reported as hydroxyl. Hencethe hydroxyl number may serve to assess the more generalreactivity/functionality of the resin. It is expressed as the mass ofpotassium hydroxide (KOH) in milligrams equivalent to the hydroxylcontent of one gram of the chemical substance, corrected for carboxylhydroxyl groups by titration of an unacetylated sample of the samematerial. Some suitable resins, e.g., polyester or polyester-basedresins, including co-polyester resins, linear and branched polyester orco-polyester resins, can have a hydroxyl value between 15 and 60,between 25 and 55, or between 35 and 50.

Additionally, a suitable resin would preferably satisfy thethermo-rheological conditions to be described in more detail in thefollowing sections. Again, such rheological patterns can be adapted tothe intended purpose. For instance, for use with printing substrateshaving low surface roughness, the viscosity of the dried ink film at ahigh temperature may be higher than the viscosity of the dried ink filmintended to adhere on a substrate having a higher surface roughness. Inother words, the ink composition to be suited for uncoated substrateswould require a relatively lower viscosity of the dried film that wouldallow the image to better follow the contour of the surface topography,hence increasing area of contact for better adherence. Generally stated,for use in the printing process herein described, the selection of theorganic polymeric (binder) resin to be included in the ink formulationsof the present disclosure may further take into account the temperatureat which the ink is jetted at the image forming station, the type ofinkjet head (such as continuous ink jet (CIJ) or drop-on-demand (DOD)),the temperature at which it contacts the intermediate transfer member,the temperature at which it is dried upon the transfer member and thetemperature at which it is transferred from the transfer member to theintended printing substrate at the impression station.

In some embodiments, suitable organic polymeric resins include acrylicpolymers, acrylic styrene copolymers, styrene polymers, polyesters. Inadditional embodiments, the resins are one or more polymers selectedfrom the group comprising Joncryl® 90, Joncryl® 530, Joncryl® 537E,Joncryl® 538, Joncryl® 631, Joncryl® 1158, Joncryl® 1180, Joncryl®1680E, Joncryl® 1908, Joncryl® 1925, Joncryl® 2038, Joncryl® 2157,Joncryl® Eco 2189, Joncryl® LMV 7051, Joncryl® 8055, Joncryl® 8060,Joncryl® 8064, Joncryl® 8067, all acrylic-based polymers available fromBASF; Dynacoll® 7150, Desmophen® XP2607 and Hoopol® F-37070, allpolyester-based polymers respectively available from Evonik, Bayer andSynthesia International, and any other commercially available chemicalequivalents thereof. For convenience, the data concerning thesematerials as provided by their respective suppliers is reproduced below.The dispersant Joncryl HPD 296 is included for comparative purposes.

Acid OH Material MW T_(g) MFFT No. No. Joncryl ® 90 >200,000 110°C.  >85° C. 76 Joncryl ® 530 75° C.  95° C. 50 Joncryl ® 537E >200,00050° C.  43° C. 52 Joncryl ® 538 >200,000 64° C.  60° C. 70 Joncryl ®631 >200,000 107° C.  >85° C. 70 Joncryl ® 1158 103° C.  Joncryl ®1180 >200,000 107° C.  >85° C. Joncryl ® 1680 E >200,000 56° C.  49° C.28 Joncryl ® 1908 98° C. >70° C. 55 Joncryl ® 1925 75° C. >70° C. 50Joncryl ® 2038 >200,000 >85° C.  >85° C. 76 Joncryl ® 2157 >200,000 105°C.  >85° C. 36 Joncryl ® Eco 2189 >200,000 98° C. >85° C. 65 Joncryl ®LMV 7051 >200,000 98° C.  56° C. 115 Joncryl ® 8055 >200,000 110°C.  >85° C. Joncryl ® 8060 >200,000 110° C.   84° C. 150 Joncryl ®8064 >200,000 97° C.  58° C. 158 Joncryl ® 8067 >200,000 110° C.  >90°C. 78 Joncryl ® HPD 296 11,500 15° C. 141 Dynacoll ® 7150 2600 50° C. <238-46 Desmophen ® 2670 ~50° C.  <2 42 XP2607 Hoopol ® F-37070 2650 51°C. <2 38-46

The molecular weight of the resin need not be limited. In someembodiments, the resin has an average molecular weight of at least1,200, at least 1,500, at least 2,000, or at least 5,000, at least25,000, at least 50,000, at least 100,000, at least 150,000, or at least200,000. In some embodiments, suitable organic polymeric resins, andparticularly polyester or polyester-based resins, including co-polyesterresins, linear and branched polyester or co-polyester resins, may havean average molecular weight of at most 12,000, at most 10,000, at most8,000, at most 6,000, at most 5,000, at most 4,000, at most 3,500, or atmost 3,000.

EXAMPLES

The following examples illustrate inkjet ink formulations according tothe teachings of the present disclosure.

Materials and chemicals were purchased from various manufacturers,including:

Air Products Air Products and Chemicals Inc., USA BASF BASF Schweiz AG,Basel, Switzerland BYK BYK-Chemie GmbH, Wesel, Germany Cabot CabotCorporation, Billerica MA, USA Clariant Clariant International Ltd,Muttenz, Switzerland Dupont DuPont de Nemours, France Dow Dow ChemicalCompany, Midland MI, USA Evonik Evonik Industries AG, Essen, GermanyHuntsman Huntsman, TX, USA Sigma-Aldrich Sigma-Aldrich Corporation, St.Louis MO, USA SKC SKC, Seoul, Korea.

Though the below formulations were prepared using materials suppliedunder the indicated trademarks of their respective manufacturer, suchingredients can be replaced by other commercially available compoundshaving similar chemical formulas.

For brevity, the below formulations are presented using Carbon Black aspigment to serve for black (K) color inks. Some of the belowformulations were prepared with cyan pigments (e.g., PV Fast Blue BG),magenta pigments (e.g., Cromophtal® Jet Magenta DMQ) or yellow pigments(e.g., Hansa Brilliant Yellow 5GX03) at the same concentrations asindicated for the black pigment, to yield respectively cyan (C), magenta(M) and yellow (Y) inks. Results obtained with black inks will bereferred to by their appropriate example number. If such results aredisplayed or discussed with reference to colors other than black, theone letter code of the specific color is indicated. For instance, ‘Ex. 4C’ will correspond to the Cyan version of the formulation disclosed inExample 4. Similarly, some of the below formulations were prepared withdyes instead of pigments. Tested dyes in conjunction with the inventiveink formulations included Basonyl® Red 485 and Basonyl® Blue 636.Alternative coloring agents (whether pigments or dyes) that may besuitable for such formulations are readily known to persons skilled inthe art of formulating printing inks.

Polymeric binder resins are commercially available in many forms,including various solid forms, such as amorphous or crystallinestructures. The resins may be available as free-flowing powders, andpellets. The resins may be available in liquid form, as emulsions ordispersions, typically blended with suitable additives. Additionally,each such commercially available resins may have a particular,characteristic particle size distribution.

As known, the viscosity of a composition can be affected by the type ofingredients it contains, their respective inherent rheologicalproperties and their concentration. As appreciated by persons skilled inthe art of ink formulation, the particle size may also affect theviscosity, to some degree, since the same amount of a material having alower particle size, provides a higher surface area available forinteractions capable of modifying some of its original physico-chemicalproperties. The particle size is, however, but one parameter, and needtherefore not be limited.

In some embodiments, the resins have an average particle size d₅₀ of 3micrometer (μm) or less, or of less than 1 μm, or of less than 0.5 μm,or of less than 400 nm, or of less than 300 nm, or of less than 200 nm,or of less than 100 nm.

A general procedure for preparing inks in accordance with embodiments ofthe invention for resins available in liquid form is as follows: first,a pigment or dye concentrate is prepared by mixing distilled water, atleast a portion (typically about 20%) of the polymeric resin ordispersant, if used, and colorant, and milling by procedure known in theart using any appropriate apparatus until a suitable particle size isreached. If a dispersant was used in this step, it was typically at a1:1 ratio with the colorant. Alternatively, commercially availablenano-pigments (e.g., having a d₅₀ below 1 μm) or sub-micron to lowmicronic range resins (e.g., having a d₅₀ below 5 μm) may be readilyused in the preparation of the ink formulations of the presentdisclosure. If a pH-raising compound is used it may be included in thisstep. The milling process was monitored on the basis of particle sizemeasurements using a dynamic light scattering particle size analyzer(e.g., ZETASIZER™ Nano-S, ZEN1600 of Malvern Instruments, England),using standard practice. Unless otherwise stated, the process wasstopped when the average particle size (d₅₀) reached about 70 nm.

The remaining materials were then added to the pigment concentrate andmixed. After mixing, the ink was filtered through a 0.5 μm filter. Theviscosity of the inks thus obtained was measured at 25° C. usingviscometer (DV II+Pro by Brookfield) and was typically in the range ofabout 2 cP to 25 cP. The surface tension was measured using a standardliquid tensiometer (EasyDyne by Krüss) and was generally in the range ofapproximately 20 to 30 mN/m. The resulting pH was usually in the rangeof 6.5 to 10.5 range, and more typically, in the range of 7.0 to 9.0.

In other embodiments, when the polymeric resin is available in solidform, an alternative procedure can be used. Typically, the resin isthoroughly milled with a dispersant, before being admixed with thecoloring agent and any other ingredient of the ink formulation. For thepreparation of some formulations herein-disclosed, a slurry consistingof 37.5 g Dynacoll® 7150 (Evonik, flakes), 93.75 g Dispex Ultra PX 4575(BASF, also known as EFKA® 4575), and 131.25 ml of distilled water wasmilled at 5° C. for 48 hours in a ball mill (Atrittor OS, Union Process,USA), having a ceramic inner surface and 0.8 mm Zirconia beads. Theground slurry was then mixed at desired ratio with a concentrate ofcoloring agent (e.g., a black pigment dispersed in a standard millingapparatus with a dispersant). In the present examples, the pigment wasdispersed with the same Dispex Ultra PX 4575 so that the final ratio ofresin to dispersant was 1:0.35. As desired, a softening agent was addedto the resin—pigment mix, and water was added if needed to achieve thefinal formulation. The fully formulated ink was then mixed and filteredthrough a 0.5 μm filter. Viscosity, surface tension and pH were measuredas mentioned hereinabove.

A partial list of the ink formulations prepared by these exemplarymethods is presented below, the content of each ingredient beingindicated in weight percent (wt. %) of the stock material, whether aliquid or solid chemical or a diluted solution, dispersion or emulsioncomprising the material of interest, the weight percent being relativeto the total weight of the final formulation. Concentrated versionshaving a solid content of at least 45% (see Example 42) and of about 80%are also provided (see Examples 40 and 41). Persons skilled in the artto which this invention pertains will readily appreciate that othermethods of preparation may be equally suitable.

Type of Material Name Wt. % Example 1 Pigment Carbon Black, Monarch ®700 2.0 Resin Joncryl ® 1680E, 43.5% emulsion in water 18.4 SofteningAgent PEG 8,000 8.0 Humectant Propylene glycol 30.0 Dispersant Joncryl ®HPD 296, 35.5% solution in water 5.6 Wetting Agent BYK ® 348 0.2 CarrierWater 35.8 Example 2 Pigment Carbon Black, Monarch ® 700 1.2 ResinJoncryl ® 1680E, 43.5% emulsion in water 11.0 Softening Agent PEG 8,0009.6 Humectant Ethylene glycol 20.0 Dispersant Joncryl ® HPD 296, 35.5%solution in water 3.4 Wetting Agent BYK ® 345 0.2 Carrier Water 54.6Example 3 Pigment Carbon Black, Monarch ® 700 2.0 Resin Joncryl ® 1680E,43.5% emulsion in water 13.8 Softening Agent PEG 8,000 6.0 HumectantEthylene glycol 30.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 5.6 Wetting Agent BYK ® 345 0.2 Carrier Water 42.4 Example 4Pigment Carbon Black, Monarch ® 700 1.3 Resin Joncryl ® 1680E, 43.5%emulsion in water 9.0 Softening Agent PEG 8,000 7.8 Humectant Propyleneglycol 20.0 Dispersant Joncryl ® HPD 296, 35.5% solution in water 3.7Wetting Agent BYK ® 345 0.2 Carrier Water 58.1 Example 5 Pigment CarbonBlack, Monarch ® 700 1.0 Resin Joncryl ® 1680E, 43.5% emulsion in water9.2 Softening Agent PEG 20,000 4.0 Humectant Propylene glycol 30.0Dispersant Joncryl ® HPD 296, 35.5% solution in water 2.8 Wetting AgentBYK ® 348 0.2 Carrier Water 52.8 Example 6 Pigment Carbon Black,Monarch ® 700 1.8 Resin Joncryl ® 1680E, 43.5% emulsion in water 12.4Softening Agent PEG 20,000 5.4 Humectant Ethylene glycol 20.0 DispersantJoncryl ® HPD 296, 35.5% solution in water 5.1 Wetting Agent BYK ® 3450.2 Carrier Water 55.1 Example 7 Pigment Carbon Black, Monarch ® 700 0.8Resin Joncryl ® 1680E, 43.5% emulsion in water 18.4 Softening Agent PEG20,000 8.0 Humectant Ethylene glycol 15.0 Dispersant Joncryl ® HPD 296,35.5% solution in water 2.3 Wetting Agent BYK ® 345 0.2 Carrier Water55.4 Example 8 Pigment Carbon Black, Monarch ® 700 0.7 Resin Joncryl ®2038, 43.5% emulsion in water 6.4 Softening Agent PEG 8,000 5.6Humectant Propylene glycol 25.0 Dispersant Joncryl ® HPD 296, 35.5%solution in water 2.0 Wetting Agent BYK 345 0.2 Carrier Water 60.1Example 9 Pigment Carbon Black, Monarch ® 700 2.0 Resin Joncryl ® 2038,43.5% emulsion in water 18.4 Softening Agent Tween ® 60 8.0 HumectantPropylene glycol 22.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 5.6 Wetting Agent Capstone ® FS-65 0.01 Carrier Water 43.97Example 10 Pigment Carbon Black, Monarch ® 700 0.9 Resin Joncryl 2038,43.5% emulsion in water 8.3 Softening Agent Tween ® 60 7.2 HumectantPropylene glycol 17.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 2.5 Wetting Agent BYK ® 345 0.2 Carrier Water 63.9 Example 11Pigment Carbon Black, Monarch ® 700 2.4 Resin Joncryl ® 8064, 43.5%emulsion in water 22.1 Softening Agent Span ® 20 2.4 Humectant Propyleneglycol 15.0 Dispersant Joncryl ® HPD 296, 35.5% solution in water 6.8Wetting Agent BYK ® 345 0.2 Carrier Water 51.2 Example 12 Pigment CarbonBlack, Monarch ® 700 1.5 Resin Joncryl ® 8064, 43.5% emulsion in water13.8 Softening Agent Span ® 20 3.0 Humectant Ethylene glycol 15.0Dispersant Joncryl ® HPD 296, 35.5% solution in water 4.2 Wetting AgentBYK ® 345 0.2 Carrier Water 62.3 Example 13 Pigment Carbon Black,Monarch ® 700 2.0 Resin Joncryl ® 8064, 43.5% emulsion in water 18.4Softening Agent PEG 8,000 8.0 Humectant Propylene glycol 25.0 DispersantJoncryl ® HPD 296, 35.5% solution in water 5.6 Wetting Agent BYK ® 3480.2 Carrier Water 40.8 Example 14 Pigment Carbon Black, Monarch ® 7001.0 Resin Joncryl ® 8064, 43.5% emulsion in water 9.2 Softening AgentPEG 8,000 8.0 Humectant Ethylene glycol 25.0 Dispersant Joncryl ® HPD296, 35.5% solution in water 2.8 Wetting Agent BYK ® 345 0.2 CarrierWater 53.8 Example 15 Pigment Carbon Black, Monarch ® 700 0.8 ResinJoncryl ® 1680E, 43.5% emulsion in water 18.4 Softening Agent PEG 8,00016.0 Humectant Ethylene glycol 5.0 Dispersant Joncryl ® HPD 296, 35.5%solution in water 2.3 Wetting Agent BYK ® 345 0.2 Carrier Water 57.4Example 16 Pigment Carbon Black, Monarch ® 700 2.0 Resin Joncryl ® 8060,45% emulsion in water 17.8 Softening Agent PEG 8,000 8.0 HumectantPropylene glycol 25.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 5.6 Wetting Agent BYK ® 348 0.2 Carrier Water 41.4 Example 17Pigment Carbon Black, Monarch ® 700 1.0 Resin Joncryl ® 8060, 45%emulsion in water 8.9 Softening Agent PEG 8,000 8.0 Humectant Ethyleneglycol 25.0 Dispersant Joncryl ® HPD 296, 35.5% solution in water 2.8Wetting Agent BYK ® 345 0.2 Carrier Water 54.1 Example 18 Pigment CarbonBlack, Monarch ® 700 1.3 Resin Joncryl ® 1680E, 43.5% emulsion in water29.9 Softening Agent PEG 8,000 13.0 Humectant Ethylene glycol 10.0Dispersant Joncryl ® HPD 296, 35.5% solution in water 3.7 Wetting AgentBYK ® 345 0.2 Carrier Water 42.0 Example 19 Pigment Carbon Black,Monarch ® 700 2.0 Resin Joncryl ® 2038, 43.5% emulsion in water 18.4Softening Agent Span ® 20 8.0 Humectant Propylene glycol 22.0 DispersantJoncryl ® HPD 296, 35.5% solution in water 5.6 Wetting Agent Capstone ®FS-65 0.01 Carrier Water 43.97 Example 20 Pigment Carbon Black,Monarch ® 700 0.9 Resin Joncryl ® 2038, 43.5% emulsion in water 8.3Softening Agent Span ® 20 7.2 Humectant Propylene glycol 17.0 DispersantJoncryl ® HPD 296, 35.5% solution in water 2.5 Wetting Agent BYK ® 3450.2 Carrier Water 63.9 Example 21 Pigment Carbon Black, Monarch ® 7001.0 Resin Joncryl ® 8060, 45% emulsion in water 8.9 Softening Agent PEG8,000 10.0 Humectant Ethylene glycol 25.0 Dispersant Joncryl ® HPD 296,35.5% solution in water 2.8 Wetting Agent BYK ® 345 0.2 Carrier Water52.1 Example 22 Pigment Carbon Black, Monarch ® 700 0.9 Resin Joncryl ®8060, 45% emulsion in water 8.0 Softening Agent PEG 8,000 9.9 HumectantPropylene Glycol 25.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 2.5 Wetting Agent BYK ® 348 0.2 Carrier Water 53.5 Example 23Pigment Carbon Black, Monarch ® 700 1.2 Resin Joncryl ® 8060, 45%emulsion in water 10.7 Softening Agent PEG 8,000 14.4 HumectantPropylene Glycol 25.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 3.4 Wetting Agent BYK ® 345 0.2 Carrier Water 45.2 Example 24 DyeBasonyl Red 485 (BASF) 1.2 Resin Joncryl ® 2038, 43.5% emulsion in water11.0 Softening Agent PEG 8,000 9.9 Humectant Ethylene Glycol 25.0Dispersant Joncryl ® HPD 296, 35.5% solution in water 3.4 Wetting AgentBYK ® 345 0.2 Carrier Water 49.3 Example 25 Pigment Carbon Black,Monarch ® 700 0.8 Resin Joncryl ® 1680E, 43.5% emulsion in water 4.6Softening Agent PEG 20,000 2.0 Humectant Ethylene glycol 15.0 DispersantJoncryl ® HPD 296, 35.5% solution in water 2.3 Wetting Agent BYK ® 3450.2 Carrier Water 75.1 Example 26 Pigment Carbon Black, Monarch ® 7001.0 Resin Joncryl ® 1680E, 43.5% emulsion in water 11.5 Softening AgentPEG 20,000 5.0 Humectant Propylene Glycol 15.0 Dispersant Joncryl ® HPD296, 35.5% solution in water 2.8 Wetting Agent BYK ® 348 0.2 CarrierWater 64.5 Example 27 Pigment Carbon Black, Monarch ® 700 2.0 ResinJoncryl ® 2038, 43.5% emulsion in water 18.4 Softening Agent Tween ® 208.0 Humectant Propylene Glycol 15.0 Dispersant Joncryl ® HPD 296, 35.5%solution in water 5.6 Wetting Agent Capstone ® FS-65 0.01 Carrier Water50.97 Example 28 Pigment Carbon Black, Monarch ® 700 2.0 Resin Joncryl ®2038, 43.5% emulsion in water 18.4 Softening Agent Tween ® 20 16.0Humectant Ethylene Glycol 20.0 Dispersant Joncryl ® HPD 296, 35.5%solution in water 5.6 Wetting Agent BYK ® 345 0.5 Carrier Water 37.48Example 29 Pigment Carbon Black, Monarch ® 700 1.5 Resin Joncryl ® 2038,43.5% emulsion in water 13.8 Softening Agent Tween ® 40 3.0 HumectantEthylene Glycol 15.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 4.2 Wetting Agent Capstone ® FS-65 0.01 Carrier Water 62.47Example 30 Pigment Carbon Black, Monarch ® 700 0.8 Resin Joncryl ® 2038,43.5% emulsion in water 7.4 Softening Agent Tween ® 40 3.2 HumectantPropylene Glycol 18.0 Dispersant Joncryl ® HPD 296, 35.5% solution inwater 2.3 Wetting Agent BYK ® 348 0.30 Carrier Water 68.1 Example 31Pigment Carbon Black, Monarch ® 700 0.9 Resin Joncryl ® 2038, 43.5%emulsion in water 8.3 Softening Agent Tween ® 40 7.2 Humectant PropyleneGlycol 15.0 Dispersant Joncryl ® HPD 296, 35.5% solution in water 2.5Wetting Agent BYK ® 345 0.20 Carrier Water 65.9 Example 32 PigmentCarbon Black, Monarch ® 700 0.7 Resin Joncryl ® 2038, 43.5% emulsion inwater 6.4 Softening Agent Tween ® 80 1.4 Humectant Ethylene Glycol 15.0Dispersant Joncryl ® HPD 296, 35.5% solution in water 2.0 Wetting AgentCapstone ® FS-65 0.01 Carrier Water 74.48 Example 33 Pigment CarbonBlack, Monarch ® 700 1.2 Resin Joncryl ® 2038, 43.5% emulsion in water11.0 Softening Agent Tween ® 80 9.6 Humectant Ethylene Glycol 15.0Dispersant Joncryl ® HPD 296, 35.5% solution in water 3.4 Wetting AgentBYK ® 345 0.20 Carrier Water 59.6 Example 34 Pigment Carbon Black,Monarch ® 700 1.0 Resin Dynacoll ® 7150 milled with EFKA ® 4575 18.5 1:1(14.38% total solids) Humectant Ethylene Glycol 15.0 Dispersant EFKA ®4575 1.7 Wetting Agent BYK ® 345 0.70 Carrier Water 63.0 Example 35Pigment Carbon Black, Monarch ® 700 1.1 Resin Dynacoll ® 7150 milledwith EFKA ® 4575 43.7 1:1 (14.38% total solids) Softening Agent Tween ®20 12.6 Humectant Propylene Glycol 15.0 Dispersant EFKA ® 4575 1.9Wetting Agent BYK ® 348 0.70 Carrier Water 25.0 Example 36 PigmentCarbon Black, Monarch ® 700 1.5 Resin Dynacoll ® 7150 milled with EFKA ®4575 59.6 1:1 (14.38% total solids) Softening Agent Tween ® 20 12.9Humectant Propylene Glycol 15.0 Dispersant EFKA ® 4575 2.6 Wetting AgentBYK ® 345 0.70 Carrier Water 7.8 Example 37 Pigment Carbon Black,Monarch ® 700 1.2 Resin Dynacoll ® 7150 milled with EFKA ® 4575 47.7 1:1(14.38% total solids) Softening Agent Tween ® 20 6.9 Humectant EthyleneGlycol 20.0 Dispersant EFKA ® 4575 2.1 Wetting Agent BYK ® 348 0.50Carrier Water 21.7 Example 38 Pigment Carbon Black, Monarch ® 700 1.0Resin Dynacoll ® 7150 milled with EFKA ® 4575 39.7 1:1 (14.38% totalsolids) Softening Agent PEG 8,000 11.4 Humectant Propylene Glycol 15.0Dispersant EFKA ® 4575 1.7 Wetting Agent BYK ® 348 0.70 Carrier Water30.4 Example 39 Pigment Carbon Black, Monarch ® 700 1.3 Resin Dynacoll ®7150 milled with EFKA ® 4575 51.7 1:1 (14.38% total solids) SofteningAgent PEG 8,000 7.4 Humectant Ethylene Glycol 20.0 Dispersant EFKA ®4575 2.2 Wetting Agent BYK ® 348 0.50 Carrier Water 16.9 Example 40Pigment Heliogen ® Blue D7092 milled with EFKA ® 8.0 4575 1:0.6 (30%total solids) Resin Joncryl ® ECO 2189 (48% nvs) as is 27.0 SofteningAgent Tween ® 80 64.8 Wetting Agent BYK ® 345 0.20 Example 41 PigmentCarbon Black, Monarch ® 700 milled with 10.0 EFKA ® 4575 1:0.6 (30%total solids) Resin Joncryl ® ECO 2189 (48% nvs) as is 26.2 SofteningAgent Span ® 20 62.8 Wetting Agent BYK ® 348 1.00 Example 42 PigmentHeliogen ® Blue D7092 milled with EFKA ® 30.0 4575 1:0.6 (30% totalsolids) Resin Joncry ®l ECO 2189 (48% nvs) as is 41.0 Softening AgentTween ® 20 19.6 Wetting Agent BYK ® 348 1.00 Carrier Water 8.40

Various commercially available nano-pigments may be used in theinventive ink formulations. These include pigment preparations such asCAB-O-JET® 352K by Cabot, Hostajet Magenta E5B-PT and Hostajet BlackO-PT, both by Clariant as well as pigments demanding post-dispersionprocesses, such as Cromophtal Jet Magenta DMQ and Irgalite Blue GLO,both by BASF.

One of ordinary skill in the art may readily recognize that variousknown colorants and colorant formulations may be used in the inventiveink or inkjet ink formulations. In one embodiment, such pigments andpigment formulations may include, or consist essentially of, inkjetcolorants and inkjet colorant formulations.

Alternatively or additionally, the colorant may be a dye. Examples ofdyes suitable for use in the ink formulations of the present inventioninclude: Duasyn Yellow 3GF-SF liquid, Duasyn Acid Yellow XX-SF, DuasynRed 3B-SF liquid, Duasynjet Cyan FRL-SF liquid (all manufactured byClariant International Ltd.); Basovit Yellow 133, Fastusol Yellow 30 L,Basacid Red 495, Basacid Red 510 Liquid, Basacid Blue 762 Liquid,Basacid Black X34 Liquid, Basacid Black X38 Liquid, Basacid Black X40Liquid (all manufactured by BASF).

Various suitable dispersants may be selected by those of skill in theart, including commercially available products. Such dispersants mayinclude high molecular weight polyurethane or aminourethane (e.g.,Disperbyk® 198), a styrene-acrylic copolymer (e.g., Joncryl® HPD 296), amodified polyacrylate polymer (e.g., EFKA® 4560, EFKA® 4580), an acrylicblock copolymer made by controlled free radical polymerization (e.g.,EFKA® 4585, EFKA® 7702), a sulfosuccinate (e.g., Triton GR, Empimin OT),an acetylenic diol (e.g., Surfynol CT), an ammonium salt of carboxylicacid (e.g., EFKA® 7571), an alkylol ammonium salt of carboxylic acid(e.g., EFKA® 5071), an aliphatic polyether with acidic groups (e.g.,EFKA 6230), or an ethoxylated non-ionic fatty alcohol (e.g., Lumiten®N-OC 30).

In some embodiments, it may be desirable to include, in addition to thepolymeric resin, colorant, water and optional co-solvent, a small amountof a surfactant, e.g., 0.5-1.5 wt. % of the ink. Such surfactants mayserve as wetting agents and/or as leveling agents. In some embodiments,the surfactant is a non-ionic surfactant. Exemplary types of wettingagents and/or leveling agents include silicones, modified organicpolysiloxanes and polyether modified siloxanes (e.g., BYK®-307,BYK®-333, BYK®-345, BYK®-346, BYK®-347, BYK®-348, or BYK®-349, from BYK,or Hydropalat WE 3240 from BASF). Fluorosurfactants such as CapstoneFS-10, Capstone FS-22, Capstone FS-31, Capstone FS-65 (DuPont),Hydropalat WE 3370, and Hydropalat WE 3500, may also be suitable.Hydrocarbon surfactants such as block copolymers (e.g., Hydropalat WE3110, WE 3130), sulfosuccinates (e.g., Hydropalat WE 3475), andacetylene diol derivatives (e.g., Hydropalat WE 3240) can be used aswetting and/or leveling agents.

In some embodiments, it may be desirable to include at least onehumectant. Examples of humectants that are miscible with water areglycols such as ethylene glycol, diethylene glycol, propylene glycol,dipropylene glycol, oligo or polyethylene glycol, oligo or polypropyleneglycol, glycerol, and glycol ethers; nitrogen containing solvents suchas N-methyl pyrrolidone and 2-pyrrolidone; and sulfur containingsolvents such as dimethyl sulfoxide (DMSO), and mixtures thereof.

Various other, or additional, dispersants, humectants, and wetting andleveling agents, which may be suitable for use in the ink formulationsof the present invention, will be apparent to those of ordinary skill inthe art.

Thermo-Rheological Properties

The inventive process in which the ink formulations can be used mayinclude the heating of the ink film or image, during transport on thesurface of the image transfer member, to evaporate the aqueous carrierfrom the ink image. The heating may also facilitate the reduction of theink viscosity to enable the transfer conditions from the ITM to thesubstrate. The ink image may be heated to a temperature at which theresidue film of organic polymeric resin and colorant that remains afterevaporation of the aqueous carrier is rendered tacky (e.g., by softeningof the resin).

Immediately prior to the transfer to the printing substrate, the residueink film on the surface of the image transfer member may be dry orsubstantially dry. The film includes the resin and the colorant from theink formulation. The residue film may further include small amounts ofone or more surfactants or dispersants, which are typically watersoluble at the pH of the ink (i.e., prior to jetting).

The ink residue film may be rendered tacky before it reaches theimpression cylinder. In this case, the film may cool at the impressionstation, by its contact with the substrate and exposure to theenvironment. The already tacky ink film may adhere immediately to thesubstrate onto which it is impressed under pressure, and the cooling ofthe film may be sufficient to reduce film adhesion to the image transfersurface to the point that the film peels away neatly from the imagetransfer member, without compromising adhesion to the substrate.

Tack (or tackiness) may be defined as the property of a material thatenables it to bond with a surface on immediate contact under lightpressure. Tack performance may be highly related to various viscoelasticproperties of the material (polymeric resin, or ink solids). Both theviscous and the elastic properties would appear to be of importance: theviscous properties at least partially characterize the ability of amaterial to spread over a surface and form intimate contact, while theelastic properties at least partially characterize the bond strength ofthe material. These and other thermo-rheological properties are rate andtemperature dependent.

Some of the significant difficulties associated with low-temperatureoperation of the Image Forming Station have been described hereinabove.Briefly, though a lower temperature at the image forming station mayreduce nozzle clogging resulting from ink carrier evaporation andprolong the lifespan of the blanket subjected then to less stringentoperating conditions, lowering the temperature of the blanket sectionunderneath this station to be below the temperature of evaporation ofthe carrier creates its own problems. While the inks need to retainjettability from the print head nozzles, the deposited droplets need toreadily adhere to the outer surface of the ITM at a viscosity that wouldbe lower than the one obtainable with the same formulation at a highertemperature, largely due to the much reduced rate of evaporation. Suchink droplets need to be able to form instantaneously, once on the ITMsurface, a skin preventing disturbance of droplet position and shape onthe blanket, as long as the ink carrier is not fully evaporated. If theadhesion needs to be facilitated by the treatment of the blanket with aconditioning solution prior to ink jetting and image formation, the typeof interaction with the optional conditioning agents may also beaffected by temperature.

The resultant ink drops subsequently undergo heating, drying, andtransfer to the printing substrate, to produce the residue ink films.These residue films, which are obtained from the ink formulations of thepresent invention, and may be processed substantially as describedherein, may have several salient features, including:

-   -   ultra-thin film thickness (typically about 0.5 μm for a        single-layer film);    -   temperature gradients: temperature variations as a function of        position along the Z-axis (thickness direction) of the film;    -   substantially or completely dry films, including the interface        between the ITM and the film surface proximal thereto; and    -   an inventive conditioning layer that may advantageously peel off        the ITM to form an integral part of the residue film.

Moreover, the process may require the inventive residue films to havesufficient flowability to readily transfer from the ITM to the printingsubstrate at low temperatures (e.g., below 140° C., below 120° C., below100° C. or below 90° C.). The process may also require the inventiveresidue films to have sufficiently low flowability at lower temperatures(e.g., below 55° C.) such that the residue films “permanently” adhere tothe printing substrate at such temperatures, without developing atendency to adhere to other surfaces.

By suitable selection of the thermo-rheological characteristics of theresidue film, the effect of the cooling may be to increase the cohesionof the residue film, whereby its cohesion exceeds its adhesion to thetransfer member so that all or substantially all of the residue film isseparated from the image transfer member and impressed as a film ontothe substrate. In this way, it is possible to ensure that the residuefilm is impressed on the substrate without significant modification tothe area covered by the film nor to its thickness.

The inventors have found that the dried or substantially dried inkresidue or ink residue film may advantageously have a first dynamicviscosity within a range of 10⁶ cP to 5·10⁷ cP for at least a firsttemperature within a first range of 60° C. to 87.5° C. The inventorshave found that such a first dynamic viscosity may be correlated withefficacious low-temperature transfer of the dried ink film from the ITMto various fibrous (e.g., coated and uncoated papers and cardboards) andnon-fibrous (e.g., various types of plastic) substrates, at extremelylow transfer pressures.

The inventors have further found that the ink residue film mayadvantageously have a second dynamic viscosity of at least 7·10⁷ cP, forat least a second temperature within a second temperature range of 50°C. to 55° C. At such viscosities and temperatures, the residue films maydisplay sufficient flowability so as to make good contact with thesurface of the printing substrate, while the surface tack, upon coolingof the ink film, is sufficiently low to discourage adhesion to othersurfaces.

Thermo-Rheological Measurements

Viscosity temperature step sweeps were performed using a ThermoScientific HAAKE Mars III rheometer having a TM-PE-P Peltier platetemperature module and a P20 Ti L measuring geometry or PP20 disposable(spindle).

Samples of substantially dry ink residue having a 1 mm depth in a 2 cmdiameter module were tested. Prior to thermo-rheological evaluation, thesamples were dried in an oven at an operating temperature of 100° C. to110° C., until the weight of the sample remained substantially constant,typically reaching the weight expected on the basis of the non-volatilematerials. Typically, the samples were dried overnight (i.e., at least12, and up to 18 hours) at 10 mbar vacuum (absolute), and were found tobe visibly and tactilely dry before being introduced to the rheometermodule.

A volume of sample (pellet) was inserted into the 2 cm diameter moduleand softened by gentle heating (typically at 80° C. for less than oneminute) to ensure adequate contact between the surface of the sample andthe spindle. The sample volume was then reduced to the desired size bylowering the spindle to reduce the sample volume to the desired depth of1 mm.

In temperature ramp mode, the sample temperature was allowed tostabilize for 120 seconds at low temperature (typically 45° C. to 55°C., in particular circa 50° C.) before being ramped up to a hightemperature (typically 150° C. to 190° C., in particular circa 180° C.).

The measurements were performed under two regimens, termed,respectively, the “long method” and “short method”. In the long method,the temperature was set to increase at a rate of approximately 0.08° C.per second up to about 110° C. and at a rate of approximately 0.04° C.per second at higher temperature (above 110° C.). Viscosity measurementswere taken at intervals of approximately 10° C., 20 repeat measurementsbeing carried out at each time point. The sample temperature was thenallowed to stabilize at high temperature for 120 seconds before beingramped down to low temperature, at the same rates. Oscillationtemperature sweeps were performed at a frequency of 1 Hz (S2=6.2832rad/sec) under a stress of 1-500 Pa up to 110° C. and at 5 Pa between110° C. and 180° C.

In the short method, the temperature was set to increase at a rate ofapproximately 0.11° C. per second up to about 110° C. and at a rate ofapproximately 0.07° C. per second at higher temperature. In the range ofup to about 110° C., viscosity measurements were taken at intervals ofapproximately 90 seconds, ten repeat measurements being carried out ateach time point. The sample temperature was then allowed to increase tothe target high temperature during 940 seconds, at which time theviscosity was last measured without ramping down back to lowertemperature. The spindle was set to oscillate at a frequency of 1 Hz.

The rheometer used in the present experimental setup provided up to tenrepeat measurements for a given temperature and for temperatures of upto 100° C., the rheometer ranked the quality of each of themeasurements, allowing trained operators to manually select, if needed,the most representative values in the linear viscous elastic range(typically at least the last three measurements in a series performed ata given temperature). Above 110° C., the samples were generally viscousand generally had a sufficient linear viscous elastic range to permitautomatic measurement.

For samples in which repeatability proves to be an issue, the sample“memory” may be reduced or substantially erased by effecting oscillationat 120° C. with 10 Pa shear force (0.5 Hz) frequency for 60 sec, taking20 points; effecting oscillation between 120° C. and 50° C. under thesame conditions, for 600 sec; effecting oscillation at 120° C. with 10Pa shear force (0.5 Hz) for 60 sec, taking 20 points

It will be appreciated by those of skill in the art that a samplematerial in which adhesion to the spindle and/or stage is insufficient,may display results that do not reflect, or fully reflect, the intrinsicthermo-rheological properties of the sample material. It will be readilyappreciated by those of skill in the art that in such a case, theviscosity must be evaluated by other available means that are suitableto the properties of the sample material.

For instance, a melt flow indexer may be used to determine the melt flowindex (MFI) of the dried ink formulations. Such apparatus monitors themass, in grams, flowing per preset period of times (e.g., in tenminutes) through a capillary of a specific diameter and length as aresult of pressure being applied via prescribed alternative gravimetricweights for alternative prescribed temperatures. Broadly speaking, themelt flow rate as measured by such method is inversely proportional tothe viscosity of the melt at the conditions of the test. Standards existfor such measurements. Such an apparatus may be used to characterize theflowability of a material as a function of several discretetemperatures.

In the specification and in the claims section that follows, values fordynamic viscosity are quantitatively determined by the “short method”described hereinabove.

Various experiments were performed in which the frequency of oscillationwas reduced from 1.0 Hz to 0.1 Hz, and/or in which the rate of increaseof temperature was raised from about 2° C. per minute, to about 10° C.per minute. Such modifications did not appreciably affect the observedthermo-rheological behavior of the samples.

Thermo-Rheological Results

FIG. 4A provides a temperature sweep plot of dynamic viscosity as afunction of temperature, for residue films of various ink formulations,including ink formulations of the present invention. The twenty plotsprovided correspond to dried ink residues of the ink formulations ofExample Nos. 1-4, 7-15, 18, 20, 23, 24, 28, 31 and 33, and the viscosityaxis spans from 1·10⁶ cP to 1·10⁹ cP. The dried ink residues wereobtained using the drying procedure provided hereinbelow.

As described above, it may be advantageous for the dried ink residues toexhibit a dynamic viscosity of at least 7·10⁷ cP, within a temperaturerange of 50° C. to 55° C. The dried ink residues may advantageouslyexhibit a dynamic viscosity of at least 8·10⁷ cP, at least 9·10⁷ cP, atleast 1·10⁸ cP, or at least 1.5·10⁸ cP. At such viscosities andtemperatures, the residue films may display good adhesion to theprinting substrate, while surface tack is sufficiently low to discourageadhesion to other surfaces.

A first rectangular window (W1), plotted in FIG. 4A, shows suitableviscosities for dried ink residues at 60° C. to about 87.5° C., withinthe temperature sweep. The inventors have found that residue filmsexhibiting good transfer properties at low temperature generally displaytemperature sweep viscosity curves that fall within this window.

A rectangular window (W2), also plotted in FIG. 4A, shows suitableviscosities for dried ink residues at 50° C. to 55° C., within thetemperature sweep. Of course, the dried ink residues may advantageouslyhave a viscosity in excess of the upper bound of the plot, i.e., 1·10⁹cP.

In the ink film constructions of the present invention, and in the inkformulations of the present invention, the temperature sweep plot ofdynamic viscosity as a function of temperature, for residue films, mayfall within both windows (W1, W2).

FIG. 4B provides temperature sweep plots of dynamic viscosity as afunction of temperature, for dried ink residues of inventive inkformulations containing various polyester resins. The plots providedcorrespond to dried ink residues of the ink formulations of Example Nos.34-39 and the viscosity axis spans from 1·10⁷ cP to 1·10⁸ cP to magnifythe area of interest. The dried ink residues were obtained using thedrying procedure provided hereinbelow.

In the ink film constructions of the present invention, and in the inkformulations of the present invention, the temperature sweep plot ofdynamic viscosity as a function of temperature, for residue filmscontaining polyester based resins, may fall within both windows (W1,W2), both shown in truncated form in FIG. 4B.

This may be more clearly demonstrated using FIG. 5, which providestemperature sweep plots of dynamic viscosity as a function oftemperature, for representative dried ink residues of various inkformulations, some of which were provided in FIGS. 4A and 4B. Near thetop left-hand corner of the graph, the temperature sweep of residue #16(of formulation #16 from Example 16) passes through W2 at a viscosity ofapproximately 1·10⁹ cP. At temperatures above 55° C., the viscosity ofresidue #16 drops monotonically. However, the slope (or negative slope)is far from sufficient for the thermo-rheological plot of residue #16 topass through W1. Similarly, the temperature sweep of residue #19 (fromExample 19) appears to pass through W2 at a viscosity above 1·10⁹ cP. Attemperatures above 55° C., the viscosity of residue #19 drops moresteeply than the viscosity of residue #16. However, the slope is stillinsufficient for the thermo-rheological plot of residue #19 to passthrough W1. However, both residue #16 and residue #19 pass through W′(not shown) a broadened, enlarged version of W1, in which the windowextends to 100° C., 105° C., or 110° C., and upward to 7·10⁷ cP, 1·10⁸cP, 2·10⁸ cP, or 3·10⁸ cP. This area of W′ is of interest, and may beutilized by means of the system, process, and ink formulations disclosedherein.

The temperature sweep of residue #2 (from the inventive ink formulationprovided in Example 2) passes through W2 at a viscosity of close to1·10⁹ cP, and at temperatures above 55° C., the viscosity dropsmonotonically. However, in contrast to the thermo-rheological behaviorexhibited by the previous examples, the slope is easily sufficient forthe thermo-rheological plot of residue #2 to pass through W1.

The temperature sweep of residue #34 (from the inventive ink formulationprovided in Example 34) passes through W2 at a viscosity of about 7·10⁷cP, and at temperatures above 55° C., the viscosity drops monotonically.However, the slope is low with respect to residue #2 and residue #19.

With reference now to residue #8 (from the inventive ink formulationprovided in Example 8), the temperature sweep passes through W2 at aviscosity approaching 2·10⁸ cP. At temperatures above 55° C., theviscosity drops monotonically, the slope being comparable to that ofresidue #2. The temperature sweep passes through a central area of W2.

Like residue #8, the temperature sweep of residue #7 (from the inventiveink formulation provided in Example 7) passes through W2 at a viscosityof around 2·10⁸ cP. At temperatures above 55° C., the viscosity dropssharply, such that the sweep passes through W1 near the bottom,left-hand corner, attaining a viscosity of 1·10⁶ cP at around 70° C.

The temperature sweep of residue #15 (from the ink formulation providedin Example 15) has a slope that is similar to that of residue #7,however, the residue has sufficiently-high flowability at lowtemperatures such that the temperature sweep falls outside the bounds ofboth W1 and W2.

The temperature sweep of residue #14 (from the ink formulation providedin Example 14) passes through W1, but at lower temperatures of 50° C. to55° C., fails to develop the requisite viscosity for dry ink residuesaccording to the present invention.

FIG. 6 provides temperature sweep plots of dynamic viscosity as afunction of temperature, for representative dried ink residues of inkformulations of the present invention, vs. dried ink residues of severalcommercially available inkjet inks. The dried ink residues of inventiveink formulations 2, 7 and 8 are those described hereinabove withreference to FIG. 5; residue #35 was obtained by drying the inventiveink formulation provided in Example 35. The commercially availableinkjet inks are black inks of Canon, Epson, HP, and Toyo, and arelabeled accordingly.

It is evident from the plots, and from the magnitude of the viscosities,that the dried ink residues of the various prior art ink formulationsexhibit no or substantially no flow behavior over the entire measuredrange of temperatures. The peaks observed at extremely high viscositiesin some plots of the prior-art formulations would appear to have nophysical meaning. Significantly, within the temperature range of 60° C.to 87.5° C., all of the prior art residue films exhibit a minimumviscosity exceeding 1·10¹⁰ cP, two and a half orders of magnitude abovethe top boundary of 5·10⁷ cP for W2.

In practice, the inventors of the present invention successfullytransferred all of the inventive ink residues to a printing substrate,but failed to transfer any of the prior-art ink films to a printingsubstrate, even after heating to over 160° C.

The transferability to printing substrates of ink formulations preparedas described in previous examples was assessed as follows: theformulations being tested were applied to the outer surface of aprinting blanket of approximately 20 cm×30 cm size on a hot platepre-heated to a predetermined surface temperature, typically between 70°C. and 130° C., the range between 70° C. and 90° C. being of particularinterest. Unless otherwise stated, this surface comprised asilanol-terminated polydimethyl-siloxane silicone (PDMS) release layer.A conditioning solution, generally comprising 0.3 wt. % ofpolyethylenimine (1:100 water diluted Lupasol® PS; PEI) in water, wasmanually applied to the release layer surface by moistening a Statitech100% polyester cleanroom wiper with the solution and wiping the releaselayer surface. The conditioning solution was then allowed to dryspontaneously on the heated blanket and the temperature of the releaselayer was monitored using an IR Thermometer Dual Laser by ExtechInstruments. Unless otherwise stated, standard transferabilityexperiments were performed at 90° C.

Thereafter, the ink formulation (e.g., about 1-2 ml) was applied andevened on the surface of the heated and optionally pre-conditionedblanket using a coating rod (e.g., Mayer rod) yielding a wet layerhaving a characteristic thickness of approximately 24 micrometers. Theink film so formed was dried with hot air (at −200° C.) until visuallydry. The dried film, while still hot, was transferred to the desiredprinting substrate, such as Condat Gloss® 135 gsm coated paper, plainoffice printer uncoated paper and plastic foils of polyester. Thesubstrate was placed on the surface of a metal roller weighing 1.5 kgand rolled over the dried ink, the transfer being performed whileapplying manual pressure equivalent to 10 kg force. The cylinder wasrolled at a pace such that 1 cm of dried ink was contacted by theprinting substrate within about 1 second.

The quality of the transferred image was visually assessed and assigneda score or rating of 0 to 5. A score of 0 indicated that less than 20%of the area of the dried ink film was transferred to the printingsubstrate, a grade of 1 indicated that between 20% and 40% of the driedink area was transferred, a grade of 2 indicated that between 40% and60% of the dried ink area was transferred, a grade of 3 indicated thatbetween 60% and 80% of the dried ink area was transferred, a grade of 4indicated that between 80% and 95% and a grade of 5 indicated that morethan 95% of the are of the dried ink area was transferred to theprinting substrate. The surface of the release layer was also observed,especially in the event of incomplete transfer. Two main types ofincomplete transfer can be observed: (a) a partial transfer, in whichonly a portion of the image transfers to the printing substrate, whereasthe complementary portion remains on the blanket; and (b) a splittransfer, in which the ink image transferring to the substrate and theink remaining on the blanket at least partially superimpose. The extentof transfer from the blanket was evaluated by the application of atransparent adhesive tape to the surface of the printing blanket and itssubsequent peeling therefrom. The area of dried ink, if any, transferredto the adhesive tape was assumed to substantially correspond to the areaof untransferred ink remaining on the blanket. A score of 0 to 5 wasassigned to estimate the percent area of dried ink remaining on theblanket. A score of 5 indicates that less than 5% of dried ink remainedon the blanket, a score of 4.5 indicates that up to 10% of the ink imageremained on the blanket, a score of 4 indicates that up to 20% of theink image remained on the blanket, a score of 3 means up to 40%, a scoreof 2 means up to 60%, a score of 1 means up to 80%, while a score of 0means up to 100% of the dried ink remained on the blanket. It is to benoted that if an ink formulation only partially transfers, the percentarea on the printing substrate and on the blanket sum up to about100%±5-10%. It is possible, however, that the summation of both valuesyields up to 200% dried ink area, in the event of complete splittingbetween the image transferring to the substrate and remaining on theblanket. Combinations of partial transfer and partial splitting are alsopossible, and are reported accordingly. An ink is considered suitablefor transfer at a particular temperature from a specific blankettreated, when necessary, with a selected conditioning agent, if thetransferability score or evaluation (transfer to the printing substrate)is at least 4.5, and preferably 5, the untransferred ink score is atleast 4.5, and preferably 5. The overall transferability rating isproduced by summing the two scores for transferred and untransferredink, and dividing by 10. A perfect score yields a rating of 1.0.

The percentage area on a surface can be visually assessed withsufficient certainty by trained operators to assign the above-describedevaluation. If necessary, the ink can be jetted to the blanket by aprinting head to deposit a test image facilitating a more quantitativeassessment of ink transferability under the operating conditions ofinterest. This can be achieved, for instance, by high resolutionscanning of the printed image and image analysis of the scan byappropriate image capturing and analysis programs

Typically, ink formulations of the present invention achieved overalltransferability ratings of at least 0.9, and more typically, 0.95 or1.0.

In some embodiments, ink formulations according to the presentteachings, deposited (e.g., either manually or by jetting) on a PDMSrelease layer heated to 90° C. and treated with PEI, can transfer to acoated fibrous printing substrate at least 90% of the area of a driedink image, at least 95%, at least 97.5%, at least 99%, or substantiallyall of the area of the image as dried on the release layer.

In some embodiments, ink formulations according to the presentteachings, deposited on a PDMS release layer heated to 90° C. andtreated with PEI can transfer to an uncoated fibrous printing substrateat least 90% of the area of a dried image, or at least 95%, or at least97.5%, or at least 99%, or substantially all of the area of the image asdried on the release layer.

In some embodiments, ink formulations according to the presentteachings, deposited on a PDMS release layer heated to 90° C. andtreated with PEI can transfer to a plastic printing substrate at least90% of the area of a dried image, or at least 95%, or at least 97.5%, orat least 99%, or substantially all of the area of the image as dried onthe release layer.

In some embodiments, ink formulations according to the presentteachings, deposited on a PDMS release layer heated to 90° C. andtreated with PEI can transfer to a coated fibrous printing substrate, orto an uncoated fibrous printing substrate, or to a plastic printingsubstrate, such that the area of a dried ink image not transferring tothe substrate is at most 5%, at most 2.5%, at most 1%, at most 0.5%, orsubstantially 0%. For each formulation, the transferability evaluationwas performed at least three times for each temperature of transferand/or printing substrate. The surface of the release layer of theblanket was cleaned with isopropanol (technical grade) and a lint-freewipe, in-between experiments. Reported results correspond to average ofrepeats under the same experimental conditions.

Softening Agents

The inventors have found that certain softening agents may be introducedto the ink formulations according to the present invention. In someembodiments of the inventive ink formulations, the addition of suchsoftening agents may enable the use of various resins exhibitingcharacteristically poor flowability at low temperatures.

As described herein, the inventors have developed a system and process,and ink formulations suitable therefor, for producing ink filmconstructions in which the transfer of the dry ink films from theintermediate transfer member to the printing substrate takes place atlow temperature, which depending on the duration of contact with and/orthe temperature of the substrate, can be between 60° C. and 140° C.,typically at the higher end of such range for printing substrates atroom temperature (circa 23° C.) contacting the ink film for a shortduration (e.g., less than 100 msec), for instance between 100° C. and130° C., and typically at the lower end of the range for printingsubstrates contacting the ink film on blanket for enough time (e.g., afew seconds) to reduce the gradient of temperature between the contactedsurfaces, for instance between 60° C. to 100° C. Other factors mayaffect optimal transfer temperatures, which may depend among otherthings from the printing system being used, the composition of theblanket release layer and conditioning solution, if any, the nature ofthe ink and substrate, their residency time of contact, the pressureapplied at the impression station, and the like.

In the printing system herein disclosed, temperatures of 40° C. to 100°C. or 70° C. to 90° C. can be used at the image forming station wherethe ink formulations are deposited on the transfer member, at whichstage the inks need to sufficiently hold to the surface of the releaselayer. Additionally, the ink formulations need be jettable at the printhead temperature, and more particularly, at the nozzle platetemperature. Typically, print heads operate at temperatures betweenabout 20° C. and about 50° C., or between about 25° C. and about 40° C.

While there exist various advantages to such low-temperature drytransfer (e.g., energy saving), significant disadvantages also exist.For example, one apparent design constraint is that the polymeric resinor binder needs to be soft to enable a dry transfer at suchtemperatures. Consequently, various mechanical properties of the printedink image or ink film construction may be compromised. The abrasionresistance may be poor, and the printed image may become sticky even atnear-ambient conditions (e.g., in a car exposed to sunlight).

Dry transfer may require a significant increase in viscosity (All)between the initial transfer temperature of the ink film and thetemperature of the film after contacting the relatively cold printingsubstrate. The inventors have found that low-temperature dry transferprocesses may require a similar substantial Δη. Moreover, the inventorshave further found that since the initial transfer temperature of thefilm is now reduced with respect to higher-temperature dry transferprocesses, the available ΔT for effecting the transfer may beappreciably reduced. In some cases, this has been found to result insplitting of the ink film during transfer, and/or excessive softness orflowability in the printed ink film product.

Resins having a relatively high T_(g) may exhibit high viscosity at suchlow temperatures, so as to substantially preclude proper transfer to theprinting substrate. As below explained, this problem is particularlyrelevant when the ink films have low total thickness (e.g., below 2.5μm), leading to rapid cooling across the film thickness and shorteningthe time window during which the viscosity of the ink film would besuitable for transfer. Thus, despite their advantageous mechanicalproperties, such high T_(g) resins may be highly unsuitable forlow-temperature, dry transfer processes, a fortiori for thin ink filmsaccording to the present teachings.

The inventors have found that softening agents may be introduced to inkformulations containing various high-T_(g) resins that would be suitablefor low-temperature ink-film transfer, if not for the high-T_(g)property. In such inventive formulations, the resin may be sufficientlyhard to inhibit, or largely inhibit, clogging of the inkjet print head,even when the blanket temperature in the vicinity of the print head is40° C.-50° C. or somewhat higher.

The softening agents may appreciably improve the flowability of a pureresin, and in the case of dry ink residue, the flowability of the driedink solids. The softening agent may be selected, and added in suitableproportion, to effect a significant reduction in the viscosity of thehigh Tg resin and/or the dried ink solids containing the high Tg resin.The viscosity may be reduced, between 60 C and 110 C, by at least 20%,at least 35%, at least 50%, at least 75%, or at least 100%, relative tothe identical high Tg resin, or dried ink solids, without the softeningagent. In many cases, the viscosity is reduced by at least 150%, atleast 200%, or at least 300%.

The selected softening agent may have a vapor pressure sufficiently lowsuch that the softening agent remains, or largely remains, in the dryink film, after the ink has been subjected to evaporation and heating.Thus, the vapor pressure of the at least one softening agent, at 150°C., may be at most 1.0 kPa, at most 0.8 kPa, at most 0.7 kPa, at most0.6 kPa, or at most 0.5 kPa. In some embodiments, however, the inventorshave found it advantageous for the vapor pressure to be even lower: atmost 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, atmost 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, atmost 0.06 kPa, or at most 0.05 kPa.

For example, such low vapor pressures may appreciably stabilize variousproperties of the ink formulation, and perhaps most notably, enable thedried ink film to retain or largely retain its transferability property,even over the course of continuous heating of the film (e.g., on theITM) for at least one hour, at least six hours, at least 24 hours, or atleast 3 days.

The inventors have found that the introduction of such softening agentsto the inventive ink formulations may compromise various mechanicalproperties of the printed image. Abrasion resistance may be reduced, andthe printed image may become sticky at near-ambient temperatures of 35°C.-45° C. The inventors have further found, however, that suchdeleterious trends may be appreciably mitigated by at least one of thefollowing:

-   -   limiting the weight ratio of softening agent to high T_(g) resin        to at most 1, at most 0.50, at most 0.40, at most 0.30, at most        0.20, at most 0.17, at most 0.15, at most 0.12, or at most 0.10;    -   limiting the weight ratio of softening agent to total resin        content to at most 0.25, at most 0.20, at most 0.15, at most        0.12, at most 0.10, at most 0.08, or at most 0.06;    -   limiting the weight ratio of softening agent to total solids        content to at most 0.20, at most 0.15, at most 0.12, at most        0.10, at most 0.08, at most 0.06, at most 0.05, or at most 0.04.

Typically, the weight ratio of softening agent to high T_(g) resin is atleast 0.02, at least 0.04, at least 0.06, at least 0.08, at least 0.10,at least 0.12, at least 0.15, or at least 0.20. The weight ratio ofsoftening agent to total resin content may be at least 0.01, at least0.02, at least 0.03, at least 0.04, at least 0.06, at least 0.08, atleast 0.10, or at least 0.12. The weight ratio of softening agent tototal solids content may be at least 0.01, at least 0.02, at least 0.03,at least 0.04, at least 0.06, at least 0.08, or at least 0.10.

Such quantities of softening agents are nonetheless substantial, andmight be expected to more severely impact mechanical properties of theprinted image. This notwithstanding, the inventors have surprisinglyfound that various affected mechanical properties of the printed imagemay remain within a suitable range. Without wishing to be bound bytheory, the inventors believe that this phenomenon may be at leastpartially attributable to the characteristically thin ink films that maybe obtained using the system and process described herein. Such thin inkfilms may have an average film thickness of at most 2.5 micrometer (μm),or at most 2.0 μm, and more typically, at most 1.8 μm, at most 1.6 μm,at most 1.4 μm, at most 1.2 μm, at most 1.0 μm, at most 0.8 μm, or atmost 0.6 μm.

While those of ordinary skill in the art may identify chemical familiesor groups that may be particularly suitable for specific resinchemistries, the inventors have discovered specific chemical familieswhose members may act as potent softening agents for a wide variety oforganic polymeric resins. These families include: low vapor pressureesters, more particularly sorbitans, polyoxyethylene sorbitans andpolysorbates; and low vapor pressure ethers, more particularlypolyethylene glycols. Exemplary compounds are Polyoxyethylene sorbitanmonolaurate, Polyoxyethylene sorbitan monopalmitate, Polyoxyethylenesorbitan monostearate, Polyoxyethylene sorbitan tristearate,Polyoxyethylene sorbitan monooleate, Polyoxyethylene sorbitan Trioleate,Sorbitan monolaurate, Sorbitan stearate, Sorbitan tristearate, Sorbitanmonooleate, Sorbitan trioleate and mid to high MW PEGs which are insolid form at room temperature. These materials are commerciallyavailable for instance as Tween® 20, Tween® 40, Tween® 60, Tween® 65,Tween® 80, Tween® 85, Span® 20, Span® 60, Span® 65, Span® 80, Span® 85,PEG 8,000, and PEG 20,000.

Such softening agents may be particularly appropriate for resinsselected from acrylic polymers, acrylic styrene copolymers, styrenepolymers, and polyesters. Exemplary compounds are commercially availableas Joncryl® 90, Joncryl® 530, Joncryl® 537E, Joncryl® 538, Joncryl® 631,Joncryl® 1158, Joncryl® 1180, Joncryl® 1680E, Joncryl® 1908, Joncryl®1925, Joncryl® 2038, Joncryl® 2157, Joncryl® Eco 2189, Joncryl® LMV7051, Joncryl® 8055, Joncryl® 8060, Joncryl® 8064, Joncryl® 8067, allacrylic-based polymers available from BASF; Dynacoll® 7150, Desmophen®XP2607 and Hoopol® F-37070, all polyester-based polymers respectivelyavailable from Evonik, Bayer and Synthesia International, and any otherchemical equivalents thereof.

The molecular weight of the softening agents used in conjunction withthe present invention may have a molecular weight of at least 300, atleast 500, at least 600, at least 700, or at least 800; the molecularweight may be at most 20,000, at most 10,000, at most 5,000, at most3,000, at most 2,500, at most 2,000, at most 1,750, at most 1,500, or atmost 1,400.

The solubility of the softening agents in water may be at least 0.1%(weight:weight of water), and more typically, at least 0.2%, at least0.3%, or at least 0.5%.

In the present application, the term softening agent is used to refer tocompounds able to significantly lower the glass transition temperatureof the resin to which it is added. The agent is said to have asignificant effect if when mixed 1:1 by solid weight with the resin ofinterest, the T_(g) of the mixture is lowered with respect to theoriginal T_(g) of the resin by at least 5° C., at least 10° C., at least15° C., at least 20° C., or at least 25° C.

By way of example, FIG. 7A displays a first plurality of temperaturesweep plots of dynamic viscosity as a function of temperature, for driedink residues of five ink formulations having identical components, and avarying ratio of softening agent, using a first thermoplastic resin(Joncryl® 1680E), and a first softening agent (polyethylene glycol (PEG)20,000). The dried residues were obtained from the ink formulationscorresponding to Examples 5, 6, 7, 25 and 26.

FIG. 7B provides a second plurality of temperature sweep plots ofdynamic viscosity as a function of temperature, for dried ink residuesof five ink formulations having identical components, and a varyingratio of softening agent, using a second thermoplastic resin, namely,Joncryl® 8060, and a second softening agent, namely, PEG 8,000. Thedried residues were obtained from the ink formulations corresponding toExamples 16, 17, 21, 22 and 23.

FIGS. 8A-8D are temperature sweep plots of dynamic viscosity as afunction of temperature, for residue films of ink formulations havingdifferent softening agents, and varying concentrations of those agents.For convenience of comparison, the pigment and the polymeric resin werethe same black pigment and Joncryl® 2038, and were kept at a 1:4 ratiofor all samples. FIG. 8A provides the thermo-rheological behavior ofdried residues of ink formulations comprising Tween® 20 (Examples27-28); FIG. 8B displays sweep plots observed for formulationscomprising Tween® 40 (Examples 29-31); FIG. 8C for formulationscomprising Tween® 60 (Examples 9-10); and FIG. 8D for formulationscomprising Tween® 80 (Examples 32-33).

In some embodiments, the softening agent may have a vapor pressure of atmost 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, atmost 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, atmost 0.06 kPa, or at most 0.05 kPa, at 150° C.

In some embodiments, the softening agent may be stable up to atemperature of at least 170° C., at least 185° C., at least 200° C., orat least 220° C.

In some embodiments, the weight ratio of the softening agent to theresin within the formulation may be at least 0.05:1, at least 0.10:1, atleast 0.15:1, at least 0.2:1, at least 0.25:1, at least 0.35:1, at least0.4:1, at least 0.5:1, at least 0.6:1, at least 0.75:1, at least 1:1, atleast 1.25:1, at least 1.5:1, at least 1.75:1, or at least 2:1.

In some embodiments, this weight ratio may be at most 3:1, at most2.5:1, at most 2:1, at most 1.6:1, or at most 1.4:1.

Various analytical methods and devices may be used to identify thevarious components of aqueous ink formulations, and the variouscomponents of the ink films produced therefrom, and these may beapparent to those of skill in the art. It may be advantageous toseparate the resins and any other polymeric materials from the aqueousphase, which contains the softening agent. The softening agent may beidentified using HPLC, MS, or other known analytical methods anddevices. The softening agent may be extracted from the resins andpolymers by various means. In one method, the resin may be swelled usingan appropriate solvent (e.g., ISOPAR), which may help to release thesoftening agent. Nanofiltration may also be appropriate in some cases.

Coloring Agents

The term “colorant” or “coloring agent”, as used herein in thespecification and in the claims section that follows, refers to asubstance that is considered, or would be considered to be, a colorantin the art of printing. The colorant may include at least one pigment.Alternatively or additionally, the colorant may include at least onedye.

As used herein in the specification and in the claims section thatfollows, the term “pigment” refers to a solid colorant, typically finelydivided. The pigment may have an organic and/or inorganic composition.Typically, pigments are insoluble in, and essentially physically andchemically unaffected by, the vehicle or medium in which they areincorporated. Pigments may be colored, fluorescent, metallic, magnetic,transparent or opaque. Pigments may alter appearance by selectiveabsorption, interference and/or scattering of light. They are usuallyincorporated by dispersion in a variety of systems and may retain theircrystal or particulate nature throughout the pigmentation process.

As used herein in the specification and in the claims section thatfollows, the term “dye” refers to at least one colored substance that issoluble or goes into solution during the application process and impartscolor by selective absorption of light.

Although a wide range of average particle sizes (d₅₀) or particle sizedistributions (PSDs) may be suitable for pigments utilized in variousembodiments of the inventive inks, the inventors believe that bestresults may be attained when the d₅₀ of the pigment is within the rangeof 20 nm to 300 nm, (e.g., at most 120 nm, at most 100 nm, or 40-80 nm).The pigments may thus be nanopigments; the particle size of thenanopigments may depend on the type of pigment and on the size reductionmethods used in the preparation of the pigments. Pigments of variousparticle sizes, utilized to give different colors, may be used for thesame print. Some pigments having such particle sizes are commerciallyavailable, and may be employed as-is in embodiments of the invention; inother cases, the pigments may be milled to the appropriate size. It willbe appreciated that in general, the pigments are dispersed (or at leastpartly dissolved) within the solvent along with the polymeric resin, orcan be first dispersed within the polymeric resin (e.g., by kneading) toobtain colored resin particles that are then mixed with the solvent.

The concentration of the at least one colorant within the inkformulation, when the formulation is substantially dry, may be at least2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, atleast 15%, at least 20%, or at least 22%, by weight. Typically, theconcentration of the at least one colorant within the ink film is atmost 40%, at most 35%, at most 30%, or at most 25%. More typically, thedry ink residue may contain 2-30%, 3-25%, or 4-25% of the at least onecolorant.

In some applications, particularly when it is desirable to have anultra-thin ink film laminated onto the printing substrate, the weightratio of the polymeric resin to the colorant may be at most 10:1, atmost 7:1, at most 5:1, at most 3:1, at most 2.5:1, at most 2:1, or atmost 1.7:1.

FIG. 9 provides temperature sweep plots of dynamic viscosity as afunction of temperature, for dried ink residues of four ink formulationshaving different colorants (C, M, Y, K) but otherwise identicalformulation components. The black formulation is as disclosed in Example4.

It will be appreciated by those of skill in the art that the inventiveformulations may be modified in a fairly predictable manner to achievedesired formulation properties, and in particular, thermo-rheologicalproperties. To this end, a large number of exemplary formulations, andthermo-rheological plots thereof, have been provided. Moreover, theplots have been arranged within the Figures to provide guidance on theeffect of resin to pigment ratio on the thermo-rheological behavior.FIG. 7A and FIG. 7B demonstrate the effect of the softening agent toresin ratio on thermo-rheological behavior, for 2 differentthermoplastic resins and 2 different softening agents. Higher softeningagent to resin ratios are generally associated with lower viscosities.Relatively hard resins may be made suitable for low-temperature transferby the softening agents. FIGS. 8A-8D demonstrate the effect of differentsoftening agents on thermo-rheological performance, combined withvarying softening agent to resin ratio, while keeping other formulationparameters constant. From the similarity of the curves in FIG. 9 it isevident that the colorants play a thermo-rheological role, but that thatrole is generally of secondary importance.

The first, “high-temperature” viscosity (associated with W1) provides ageneral indication of film transfer properties, which is important inthe transfer of the film from the release layer of the ITM. The maximumviscosity value associated with that physical property may berepresented by the top line or area of W1.

The second, “low-temperature” viscosity (associated with W2 at 50-55°C.) provides a general indication of how the film will behave on theprinting substrate. The minimum viscosity value associated with thatphysical property may be represented by the bottom of W2.

With respect to the drying of inks for thermo-rheological testing of dryink samples, the inventors have used various rigorous procedures andoperating conditions to ensure that the ink residues attain a sufficientlevel of dryness to enable comparative testing between samples and toachieve good repeatability of thermo-rheological results for dried inkresidues produced from an identical ink formulation.

The inventors have found that some of these rigorous procedures andoperating conditions may be relaxed without appreciably impinging uponthermo-rheological repeatability, such that the following definition ofink residue dryness may be utilized: as used in the Specification and inthe claims section that follows, the term “substantially dry”, and thelike, with regard to an ink residue, refers to an ink residue, obtainedby drying of a particular ink, the ink residue preferably containing nomore solvent and other volatile compounds than does a “standard” layerof that particular ink, having a 1 mm initial thickness, after suchlayer is dried in an oven for 12 hours at 100° C. and at 10 mbar vacuum(absolute). In the case of inks that prove difficult to dry, the depthof the vacuum may be increased to 5 mbar. In the case of inks that proveparticularly difficult to dry, the ink residue may be allowed to exhibita % loss-on-drying (LOD) of up to 1% or up to 2% below the % LODexhibited by the “standard” layer.

Similarly, an ink formulation dried to form a “substantially dried” inkresidue is termed “substantially dried”.

In some embodiments, the ink formulation is devoid or substantiallydevoid of wax. Typically, the ink formulation contains less than 30 wt.% wax, less than 20 wt. % wax, less than 15 wt. % wax, less than 10 wt.% wax, less than 7 wt. % wax, less than 5 wt. % wax, less than 3 wt. %wax, less than 2 wt. % wax, or less than 1 wt. % wax. In otherembodiments, wax is included in the ink formulation in order to impartgreater abrasion resistance in the printed ink. Such waxes may benatural or synthetic, e.g., based on esters of fatty acids and fattyalcohols or long-chain alkanes (paraffin waxes), or mixtures thereof. Insuch cases, the formulation may comprise, for example, 0.1-10 wt. % wax,e.g., up to 0.1, 0.3, 0.5, 0.7, 1.0, 1.5, 2, 3, 4, 6, 8, or 10 wt. %wax. The wax may be incorporated into the formulation as an aqueousdispersion of small wax particles, e.g., having an average size of 10micrometers or smaller, preferably having average size of 1 μm orsmaller.

In some embodiments, the ink formulation is devoid or substantiallydevoid of oils such as mineral oils and vegetable oils (e.g., linseedoil and soybean oil). Typically, the ink formulation contains at most 20wt. %, at most 12 wt. %, at most 8 wt. %, at most 5 wt. %, at most 3 wt.%, at most 1 wt. %, at most 0.5 wt. %, or at most 0.1 wt. %, by weight,of one or more oils, cross-linked fatty acids, or fatty acid derivativesproduced upon air-drying.

In some embodiments, the ink formulation is devoid or substantiallydevoid of glycerol. Typically, the ink formulation contains at most 10%,at most 8%, at most 6%, at most 4%, at most 2%, at most 1%, at most0.5%, or at most 0.2% glycerol, by weight.

In some embodiments, the ink formulation is devoid or substantiallydevoid of one or more salts, including salts used to coagulate orprecipitate ink on a transfer member or on a substrate (e.g., calciumchloride). Typically, the ink formulation contains at most 8 wt. %, atmost 5 wt. %, at most 3 wt. %, at most 1 wt. %, at most 0.5 wt. %, atmost 0.1 wt. %, or substantially 0 wt. % of one or more salts. Suchsalts may be referred to herein as “precipitants”, and it will beappreciated that when it is stated that a formulation does not include asalt or contains salt in an amount less than a certain weightpercentage, this does not refer to salts that may form between thepolymer(s) of the polymeric resin and pH modifiers, such as alcoholamines, or that may be present in the polymeric resin itself if thepolymeric resin is provided as a salt. As discussed above, it ispresently believed that the presence of negative charges in thepolymeric resin is beneficial to the print process.

In some embodiments, the ink formulation is devoid or substantiallydevoid of inorganic particulates, e.g., silica particulates, titaniaparticulate or alumina particulates, containing less than 2 wt. %, lessthan 1 wt. %, less than 0.1 wt. % or substantially no inorganicparticulates. By “silica particulates” is meant fumed silica, silicachips, silica colloids, and the like. Specific examples of such silicaparticulates include those available from DuPont Company under thenames: Ludox® AM-30, Ludox® CL, Ludox® HS-30; and those available fromNyacol Nanotechnologies Company under the names: NexSil™ 12, NexSil™ 20,NexSil™ 8, NexSil™ 85. In the context of the present application, theterm “silica particulates” does not include colorants.

Ink Film Constructions

In the ink film constructions of the present invention, the ink dot mayessentially be laminated onto a top surface of the printing substrate.As described herein, the form of the dot may be determined or largelydetermined prior to the transfer operation, and the dot is transferredas an integral unit to the substrate. This integral unit may besubstantially devoid of solvent, such that there may be no penetrationof any kind of material from the blanket transfer member into, orbetween, substrate fibers. The continuous dot, which may largely containorganic polymeric resin and colorant, adheres to, or forms a laminatedlayer on, the top surface of the fibrous printing substrate.

Printing tests employing the afore-disclosed ink compositions show goodtransfer to various and varied paper and plastic substrates, as will beillustrated in some of the following Figures.

FIGS. 10A-F display two-dimensional (FIGS. 10A-C) and three-dimensional(FIGS. 10D-F) laser-microscope acquired magnified images of ink films oncommodity-coated paper substrates, obtained using various printingtechnologies, wherein: FIGS. 10A and 10D are magnified images of aliquid electro-photography film (LEP); FIGS. 10B and 10E are magnifiedimages of an offset splotch; and FIGS. 10C and 10F are magnified imagesof an inkjet ink film construction according to the present invention.The laser microscopy imaging was performed using an Olympus LEXT 3Dmeasuring laser microscope, model OLS4000.

FIGS. 11A-F display two-dimensional (FIGS. 11A-C) and three-dimensional(FIGS. 11D-F) laser-microscope acquired magnified images of ink films onuncoated paper substrates, obtained using various printing technologies,wherein: FIGS. 11A and 11D are magnified images of a liquidelectro-photography film (LEP); FIGS. 11B and 11E are magnified imagesof a lithographic offset splotch; and FIGS. 11C and 11F are magnifiedimages of an inkjet ink film construction according to the presentinvention.

The ink dots in the ink dot constructions of the present invention mayexhibit consistently good shape properties (e.g., roundness, edgeraggedness, and the like), irrespective, to an appreciable degree, ofthe particular, local topographical features of the substrate, andirrespective, to an appreciable degree, of the type of printingsubstrate (coated or uncoated printing substrates, plastic printingsubstrates, etc.).

By contrast, the quality of ink dots in various known printingtechnologies, and in direct aqueous inkjetting technologies inparticular, may vary significantly with the type of printing substrate,and with the particular, local topographical features of the substrate.It will be readily appreciated that, by way of example, when an ink dropis jetted onto a particularly flat local contour having a relativelyhomogeneous substrate surface (such as a broad fiber), the ink dotobtained may display significantly better shape properties, with respectto the other, or average ink dots disposed elsewhere on the substrate.

In these prior art ink and substrate constructions, the inkjet ink dropshave penetrated the surface of the paper, as may be best seen in FIGS.11D-11F. Such penetration may be typical of various printingtechnologies using uncoated or commodity-coated paper, in which thepaper may draw ink carrier solvent and pigment within the matrix of thepaper fibers.

In contrast to these prior art ink constructions, the inventive inkjetink film constructions may be characterized by well-defined individualink films, disposed generally above, and adhering to, the fibroussubstrates, both coated (FIGS. 10C, 10F) and uncoated (FIGS. 11C, 11F).

The inventive inkjet single-drop ink film (or individual ink dot)construction was produced using the inventive system and methoddescribed herein, using an ink formulation Example 29 according to thepresent invention.

Dot Perimeter Characterization

The perimeter of the offset ink splotch and the perimeter of the LEP inksplotch have a plurality of protrusions or rivulets, and a plurality ofinlets or recesses. These ink forms may be irregular, and/ordiscontinuous. By contrast, the inkjet ink dot produced according to thepresent invention, best seen in FIGS. 10C and 11C, has a manifestlyrounded, convex, shape. The perimeter of the ink film is relativelysmooth, regular, continuous and well defined.

More particularly, projections of the ink film of the invention againstthe substrate surface (i.e., projections from a top view) tend to berounded, convex projections that form a convex set, i.e., for every pairof points within the projection, every point on the straight linesegment that joins them is also within the projection. Such a convex setis shown in FIG. 15A. By sharp contrast, the rivulets and inlets in theprojections of various prior-art define those projections as anon-convex sets, i.e., for at least one straight line segment within aparticular projection, a portion of that straight line segment isdisposed outside the projection, as illustrated in FIG. 15B.

It must be emphasized that ink images may contain an extremely largeplurality of individual or single ink films. For example, a 5 mm by 5 mmink image, at 600 dpi, may contain more than 10,000 of such single inkfilms. Therefore, it may be appropriate to statistically define the inkfilm constructions of the present invention: at least 10%, at least 20%,or at least 30%, and more typically, at least 50%, at least 70%, or atleast 90%, of the single ink dots (selected at random), or projectionsthereof, may be convex sets.

It must be further emphasized that ink images may not have crispboundaries, particularly when those boundaries are viewed at highmagnification. Therefore, it may be appropriate to relax the definitionof the convex set whereby non-convexities (rivulets or inlets) having aradial length L_(r) (as shown in FIG. 15C) of up to 3,000 nm, up to1,500 nm, up to 1,000 nm, up to 700 nm, up to 500 nm, up to 300 nm, orup to 200 nm, are ignored, excluded, or are “smoothed”, whereby the inkfilm or ink film projection is considered to be a convex set. The radiallength L_(r) is measured by drawing a radial line L from the centerpoint C of the ink film image, through a particular rivulet or inlet.The radial length L_(r) is the distance between the actual edge of therivulet or inlet, and a smoothed projection P_(s) of the ink image,devoid of that rivulet or inlet, and matching the contour of the inkfilm image.

In relative terms, it may be appropriate to relax the definition of theconvex set whereby non-convexities (rivulets or inlets) having a radiallength of up to 15% of the film/drop/splotch diameter or averagediameter, up to 10%, and more typically, up to 5%, up to 3%, up to 2%,or up to 1%, are ignored, excluded, or are “smoothed”, as above, wherebythe ink film or ink film projection is considered to be a convex set.

The perimeter of various ink dots or films of the prior art maycharacteristically have a plurality of protrusions or rivulets, and aplurality of inlets or recesses. These ink forms may be irregular,and/or discontinuous. By sharp contrast, the inkjet ink dot producedaccording to the present invention characteristically has a manifestlyrounded, convex, circular shape. The perimeter of the ink dot of theinvention may be relatively smooth, regular, continuous and welldefined. Ink dot roundness, convexity, and edge raggedness arestructural parameters used to evaluate or characterize shapes, oroptical representations thereof.

It can readily be observed, by comparing the magnified images of theprior-art ink forms of FIGS. 10A and 10B with the inventive ink dotconstruction of FIG. 10C, or by comparing the magnified images of theprior-art ink forms of FIGS. 11A and 11B with the inventive ink dotconstruction of FIG. 11C, that the appearance of the ink dots of thepresent invention is manifestly distinct from these prior-art ink forms.That which is readily observed by the human eye may be quantified usingimage-processing techniques. Various characterizations of the ink formsare described hereinbelow, after a description of the image acquisitionmethod.

Acquisition Method

(1) For each of the known printing technologies to be compared in thestudy, single dots, splotches, or film images printed on coated paperand on uncoated paper were used, including numerous coated and uncoatedfibrous substrates, and various plastic printing substrates.

(2) With regard to the printing technology according to the presentinvention, single drop dot images were printed on coated paper and onuncoated paper. Care was taken to select substrates having similarcharacteristics to the substrates of the known ink-dot constructionsused in (1).

(3) The acquisition of the dot images was performed using an OLS4000(Olympus) microscope. Those of ordinary skill in the art know how toadjust the microscope to achieve the requisite focus, brightness andcontrast, so that the image details will be highly visible. These imagedetails include the dot contour, the color variance within the dot area,and the fibrous structure of the substrate surface.

(4) The images were taken with an X100 optical zoom lens having aresolution of 129 micrometers×129 micrometers. This high resolution maybe essential in obtaining fine details of the dot and of the fibrousstructure of the substrate surface.

(5) The images were saved in uncompressed format (Tiff) having aresolution of 1024×1024 pixels, as image data may be lost incompression.

(6) Generally, a single dot or splotch was evaluated for each printingtechnology. From a statistical point of view, however, it may beadvantageous to obtain 15 dot images (at least) for each type ofhard-copy print being analyzed, and to manually select the 10 (at least)most representative dot images for image processing. The selected dotimages should be representative in terms of dot shape, contour and colorvariation within the dot area. Another approach to print dot sampling,termed “field of view”, is described hereinbelow.

Dot Contour Computation

The dot images were loaded to the image-processing software(ImageXpert). Each image was loaded in each of the Red, Green and Bluechannels. The processing channel was selected based on a highestvisibility criterion. For example, for cyan dots, the Red channeltypically yielded the best dot feature visibility, and was thus selectedfor the image processing step; the Green channel was typically mostsuitable for a magenta dot. The dot edge contour was detected(automatically computed), based on a single threshold. Using a “fullscreen view” mode on a 21.5″ display, this threshold was chosen manuallyfor each image, such that the computed edge contour would best match thereal and visible dot edge. Since a single image-channel was processed,the threshold was a gray value (from 0 to 255, the gray value being anon color value).

A computed perimeter value was obtained from the image-processingsoftware (e.g., ImageXpert), the perimeter value being the sum of alldistances between the adjacent, connected pixels at the edge of the dotor splotch. If, for example, the XY coordinates for adjacent pixels are(x1, y1) and (x2, y2), the distance is √[(x2−x1)²+(y2−y1)²], while theperimeter equals Σ{√[(x_(i+1)−x_(i))²+(y_(i+1)−y_(i))²]}.

In various embodiments of the invention, it is desired to measure thelength of the perimeter of an ink dot. An alternative method formeasuring the perimeter length will now be described. As a first step,an image comprising an ink dot is used as input for an algorithm thatoutputs perimeter length. The pixel dimension M×N of the image may bestored in a two-element array or an ordered pair image_pixel_size. Anexample of the value of the image_pixel_size is 1280,760—in this exampleM=1280 and N=760. This corresponds to an image 1280 pixels in thehorizontal axis and 760 pixels in the vertical axis. Subsequently, theimage magnification ratio or scale is obtained and stored in variableimage_magnification. One example of variable image_magnification is 500.When comparing perimeters between ink dots in first and second images itis mandatory that the variables image_pixel_size and image_magnificationof the two images are equal. It is now possible to calculate thecorresponding length of one square pixel—i.e. the side length in areal-world length units (e.g., micrometers) or a pixel. This value isstored in a variable pixel_pitch. One example of the variablepixel_pitch is 0.05 μm. The image is now converted to grayscale bymethods known to the skilled artisan. One proposed method is convertingthe input image, the image typically in an sRGB color space, to theL*a*b* color space. Once the image is in the Lab color space, the valuesfor the variables a and b are changed to zero. It is now possible toapply an edge detection operator to the image. The preferred operator isa Canny edge detection operator. However, any operator known in the artmay be applied. The operators are not limited to first orderderivatives, such as the canny operator, but rather open to secondderivatives as well. Furthermore, a combination of operators may be usedin order to obtain results that may be compared between operators andsubsequently remove “unwanted” edges. It may be favorable to apply asmoothing operator such as a Gaussian blur prior to applying the edgedetection operator. The threshold level applied when applying the edgedetection operator is such that an edge that forms an endless loop isfirst obtaining in the area between the formerly described minimalcircumference Ink dot engulfing circle and the maximal circumference inkdot enclosed circle. A thinning operator is now implemented to renderthe endless loop edge substantially one pixel wide. Any pixel that isnot a part of the endless loop edge has its L* value change to zero,while any pixel that is part of the endless loop edge has its L* valuechange to 100. The endless loop edge is defined as the perimeter of theink dot. A pixel link is defined as a straight line connecting topixels. Each pixel along the perimeter incorporates two pixel links, afirst pixel link and a second pixel link. These two pixel links define apixel link path within a single pixel. In this method of computingperimeter length, each pixel is a square pixel. Therefore, each pixellink may form a line from the center of the pixel to one of eightpossible nodes. The possible nodes being the corners of the pixel or amidpoint between two neighboring corners of the pixel. Nodes at thecorners of the pixels are of the type node_1 one nodes at the midpointbetween two corners are of type node_2. As such, there are sixpossibilities of pixel link paths within a pixel. These can becategorized into three groups. Group A, B, and C. Each group has its owncorresponding coefficient, namely, coefficient_A, coefficient_B, andcoefficient_C. The value of coefficient_A is 1, the value ofcoefficient_B is the sqrt(2), and the value of coefficient_C is(1+sqrt(2))/2. Group A contains pixels whose pixel link path coincideswith nodes of type node_2. Group B contains pixels whose pixel link pathcoincides with nodes of type node_1. Group C contains pixels whose pixellink path coincides with nodes of type node_1 and type node_2. It is nowpossible to calculate the pixel length of the perimeter. The pixellength of the perimeter is calculated by summing all of the pixels inthe perimeter multiplied by their corresponding coefficient. This valueis stored in variable perimeter_pixel_length. It is now possible tocalculate the actual length of the ink dot perimeter. This is done bymultiplying perimeter_pixel_length by pixel_pitch.

Roundness

A dimensionless roundness factor (ER), may be defined by:

ER=P ²/(4π·A)

wherein P is the measured or calculated perimeter, and A is the measuredor computed area within the ink film, dot or splotch. For a perfectlysmooth and circular ink dot, ER equals 1.

The deviation from a round, smooth shape may be represented by theexpression (ER−1). For a perfectly circular, idealized ink dot, thisexpression equals zero.

The R-square of the roundness factor may be computed for each of the 10most representative dot images selected for each type of printingtechnology, and averaged into a single value.

For ink film constructions in which the fibrous substrate (e.g., paper)is uncoated, or for ink film constructions in which the fibroussubstrate is coated with a coating such as the commodity coating incoated offset paper (or such as coatings which enable the carrier fromtraditional water-based inkjet ink to reach the paper fibers), thedeviation from a round, smooth round shape [(ER−1), henceforth,“deviation”] for the ink dots of the present invention is not ideal, andwill exceed 0.

In FIGS. 14A-2 to 14F2, exemplary magnified ink film images disposed onuncoated and coated substrates are provided for the following printers:direct inkjet: HP DeskJet 9000 (uncoated: FIG. 14A-2; coated: FIG.14D-2); digital press: HP Indigo 7500 (uncoated: FIG. 14B-2; coated:FIG. 14E-2); and lithographic offset: Ryobi 755 (uncoated: FIG. 14C-2;coated: FIG. 14F-2).

FIGS. 12A-2 to 12E-2 provide magnified views of ink films disposed oncoated paper (12A-2 to 12C-2) and uncoated paper (12D-2 and 12E-2),according to the present invention. These ink film images were obtainedgenerally according to the image acquisition method detailedhereinabove.

Quantitative analysis of the deviation from roundness (ER−1) is providedhereinbelow.

Convexity

As previously described, the ink dots or films of the prior art maycharacteristically have a plurality of protrusions or rivulets, and aplurality of inlets or recesses. These ink forms may be irregular,and/or discontinuous. By sharp contrast, the inkjet ink film producedaccording to the present invention characteristically has a manifestlyrounded, convex, circular shape. Dot convexity, or deviation therefrom,is a structural parameter that may be used to evaluate or characterizeshapes, or optical representations thereof.

The image acquisition method may be substantially identical to thatdescribed hereinabove.

Convexity Measurement

The dot images were loaded to the image-processing software(ImageXpert). Each image was loaded in each of the Red, Green and Bluechannels. The processing channel was selected based on a highestvisibility criterion. For example, for cyan dots, the Red channeltypically yielded the best dot feature visibility, and was thus selectedfor the image processing step; the Green channel was typically mostsuitable for a magenta dot. The dot edge contour was detected(automatically computed), based on a single threshold. Using a “fullscreen view” mode on a 21.5″ display, this threshold was chosen manuallyfor each image, such that the computed edge contour would best match thereal and visible dot edge. Since a single image-channel was processed,the threshold was a gray value (from 0 to 255, the gray value being anon color value).

A MATLAB script was created to compute the ratio between the area of theminimal convex shape that bounds the dot contour and the actual area ofthe dot. For each ink dot image, the (X,Y) set of points of the dot edgecontour, created by ImageXpert, was loaded to MATLAB.

In order to reduce the sensitivity of measurement to noise, the dot edgewas passed through a Savitzky-Golay filter (image-processing low-passfilter) to slightly smooth the edge contour, but without appreciablymodifying the raggedness characteristic thereof. A window frame size of5 pixels was found to be generally suitable.

Subsequently, a minimal-area convex shape was produced to bound thesmoothed edge contour. The convexity ratio between the convex shape area(CSA) and the actual (calculated) dot or film area (AA) was thencomputed as follows:

CX=AA/CSA

The deviation from this convexity ratio, or “non-convexity”, isrepresented by 1−CX, or DC_(dot).

Quantitative analysis of this non-convexity is provided hereinbelow.

Field of View

On both commodity-coated and uncoated fibrous substrates, the ink dotsin the ink dot constructions of the present invention may exhibitconsistently good shape properties (e.g., convexity, roundness, edgeraggedness, and the like), irrespective, to a large degree, of theparticular, local topographical features of the substrate, andirrespective, to some degree, of the type of printing substrate (coatedor uncoated printing substrates, plastic printing substrates, etc.). Bycontrast, the quality of ink dots in various known printingtechnologies, and in direct aqueous inkjetting technologies inparticular, may vary appreciably with the type of printing substrate,and with the particular, local topographical features of the substrate.

Using a more robust, statistical approach, however, may betterdistinguish between the inventive ink dot constructions with respect toink dot constructions of the art. Thus, in some embodiments of thepresent invention, the ink dot constructions may be characterized as aplurality of ink dots disposed on the substrate, within a representativefield of view. Assuming the characterization of the dot is obtainedthrough image processing, a field of view contains a plurality of dotimages, of which at least 10 dot images are suitable for imageprocessing. Both the field of view and the dot images selected foranalysis are preferably representative of the total population of inkdots on the substrate (e.g., in terms of dot shape).

Procedure

A printed sample, preferably containing a high incidence of single inkdots, is scanned manually on the LEXT microscope, using a X20magnification to obtain a field that includes at least 10 single dots ina single frame. Care should be taken to select a field whose ink dotquality is fairly representative of the overall ink dot quality of theprinted sample.

Each dot within the selected frame is analyzed separately. Dots that are“cleaved” by the frame margins (which may be considered a squaregeometric projection) are considered to be part of the frame, and areanalyzed. Any satellites and overlapping dots are excluded from theanalysis. A “satellite” is defined as an ink dot whose area is less than25% of the average dot area of the dots within the frame, for frameshaving a generally homogeneous dot size, or as an ink dot whose area isless than 25% of the nearest adjacent dot, for non-homogeneous frames.

Each distinct ink dot is subsequently magnified with a X100 zoom, andimage processing may be effected according to the procedure providedhereinabove with respect to the convexity and roundness procedures.

Results

FIG. 13A provides a magnified view of a field of ink dots on acommodity-coated fibrous substrate (Arjowiggins coated recycled gloss,170 gsm), produced using a commercially available, aqueous, directinkjet printer. FIG. 13B provides a magnified view of a field of inkdots on an uncoated fibrous substrate (Hadar Top uncoated-offset 170gsm), produced using the identical, commercially available, aqueous,direct inkjet printer. Although technically, the frame of FIG. 13A doesnot qualify as a “field” of ink dots, such fields requiring at least 10single dots within a single frame, the frames are provided, and the dotsare characterized, for illustrative purposes.

In FIG. 13A, ink image A is a satellite, and is excluded from theanalysis. Dot B is cleaved by the frame margin, and is included in theanalysis (i.e., the full ink dot is analyzed). Tail or projection C isconsidered to be part of the ink dot disposed to its left. Thus, thefield contains only 6 ink dots for image processing.

With regard to FIG. 13B, it became evident, only at high magnification,that dots E and F are distinct individual dots. While several splotchesare reasonably round and well-formed, most of the splotches display poorroundness and convexity, have poorly-defined edges, and appear tocontain multiple ink centers that are associated or weakly associated.

FIGS. 12A-1 to 12E-1 provide a magnified view of a field of ink dots orfilms on commodity-coated fibrous substrates (FIGS. 12A-1 to 12C-1) anduncoated fibrous substrates (FIGS. 12D-1 and 12E-1), produced inaccordance with the present invention. The printed image was prepared byjetting an ink, corresponding to Example 29, on a blanket having arelease layer comprising a condensation cured silanol terminatedpolydimethylsiloxane. The blanket was heated to about 70° C. and waspre-treated with a conditioning solution comprising PEI subsequentlyremoved and evaporated, as already described for the basictransferability test. A black ink corresponding to Example 29 was jettedupon the treated release layer using a traditional ink jet head at aresolution of 600×1200 dpi (providing an average drop volume of 9 pL) toform an ink image of varying ink coverage/dot density. The relativespeed of the blanket relative to the print bars was 0.5 m/sec. The inkimage was dried at 200° C. for up to 5 seconds and the dried imagetransferred to the substrates indicated in the table below and in FIGS.12A-1 to 12E-3, by application of manual pressure.

FIGS. 12A-2 to 12E-2 provide further magnified views of a portion of theframes of FIGS. 12A-1 to 12E-1, in which the magnified views of the inkfilms disposed on commodity-coated paper are provided in FIGS. 12A-2 to12C-2, and the magnified views of the ink films disposed on uncoatedpaper are provided in FIGS. 12D-2 and 12E-2.

It is manifest from a comparison of the figures that the fields of inkdots in the inventive ink constructions exhibit superior dot shape(roundness, convexity, and edge definition) and average dot shape, withrespect to the prior-art fields provided in FIGS. 13A and 13B. In fact,the field of ink dots provided in FIG. 12D-1, in which the uncoatedsubstrate is the most coarse and challenging, the inventive inkconstruction exhibits superior dot shape and average dot shape, relativeto the prior-art field (FIG. 13A) in which the substrate is a relativelysmooth, coated substrate.

That which is readily observed by the human eye may be quantified usingthe image-processing techniques and field-of-view processing proceduresprovided above.

TABLE 1 Inventive Ink Dot Constructions -- Field of View OpticalUniformity Manufacturer Brand Name or (Standard Name Paper Type GSM ER-11-CX Deviation) SAPPI MAGNO Gloss 170 0.096 0.0044 2.01 Star SAPPI MAGNOSatin 170 0.126 0.0055 2.21 DALUM DALUM Gloss 250 0.110 0.0046 2.65Recycled Fedrigoni Uncoated 400 0.305 0.0220 4.70 UPM Fine Offset 2500.276 0.0180 4.62 Uncoated

TABLE 2 Prior Art Ink Dot Constructions -- Field of View OpticalUniformity Substrate Type ER-1 1-CX (Standard Deviation) Coated Paper0.943 0.085 4.0 Uncoated Paper 3.347 0.253 19.1

These exemplary results have been confirmed on several additionalfibrous substrates, both commodity-coated and uncoated.

For all tested commodity-coated fibrous substrates, fields of the inkdot construction according to the present invention exhibited a meannon-convexity of at most 0.05, at most 0.04, at most 0.03, at most0.025, at most 0.020, at most 0.015, at most 0.012, at most 0.010, atmost 0.009, or at most 0.008.

For all tested uncoated fibrous substrates, fields of the ink dotconstruction according to the present invention exhibited a meannon-convexity of at most 0.085, at most 0.07, at most 0.06, at most0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.020, at most0.018, or at most 0.015.

In some embodiments, the field non-convexity is at least 0.0005, atleast 0.001, at least 0.002, at least 0.003, or at least about 0.004. Insome cases, and particularly for uncoated fibrous substrates, the fieldor mean non-convexity may be at least 0.05, at least 0.07, at least0.10, at least 0.12, at least 0.15, at least 0.16, at least 0.17, or atleast 0.18.

For all tested commodity-coated fibrous substrates, fields of the inkdot construction according to the present invention exhibited a meandeviation from roundness of at most 0.60, at most 0.50, at most 0.45, atmost 0.40, at most 0.35, at most 0.30, at most 0.25, at most 0.20, atmost 0.17, at most 0.15, at most 0.12, or at most 0.10.

For all tested uncoated fibrous substrates, fields of the ink dotconstruction according to the present invention exhibited a meandeviation from roundness of at most 0.85, at most 0.7, at most 0.6, atmost 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most0.22, or at most 0.20.

In some embodiments, the mean deviation from roundness is at least0.010, at least 0.02, at least 0.03, or at least about 0.04. In somecases, the deviation from roundness may be at least 0.05, at least 0.07,at least 0.10, at least 0.12, at least 0.15, at least 0.16, at least0.17, or at least 0.18.

While the above-described non-convexity and deviation from roundnessvalues are for fields having at least 10 dots suitable for evaluation,they further apply to fields having at least 20, at least 50, or atleast 200 of such suitable dots. Moreover, the inventors have found thatthe distinction between both the non-convexity values and deviation fromroundness values of the inventive ink dot constructions vs. theprior-art ink dot constructions becomes even more statisticallysignificant with increasing field size.

For plastic substrates, the fields of the ink dot construction accordingto the present invention can exhibit a mean non-convexity of at most0.075, at most 0.06, at most 0.05, at most 0.04, at most 0.03, at most0.025, at most 0.020, at most 0.015, at most 0.012, at most 0.010, atmost 0.009, or at most 0.008; the fields of the ink dot constructionaccording to the present invention may exhibit a mean deviation fromroundness of at most 0.8, at most 0.7, at most 0.6, at most 0.5, at most0.4, at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most0.18, or at most 0.15. Smooth plastics, such as atactic polypropyleneand various polyesters, typically exhibit a mean deviation fromroundness of at most 0.35, at most 0.3, at most 0.25, at most 0.20, atmost 0.18, at most 0.15, at most 0.12, at most 0.10, at most 0.08, atmost 0.06, at most 0.05, at most 0.04, or at most 0.035.

Optical Uniformity

The ink film images provided in FIGS. 5A and 5B are not opticallyuniform. Generally, the ink film images disposed on uncoated paper areless optically uniform than the corresponding ink film images disposedon coated paper.

Furthermore, it can be observed that the inventive ink dots exhibitsuperior optical uniformity in comparison with the various prior-art inkforms. This appears to hold for both uncoated and coated printedsubstrates. That which is readily observed by the human eye may bequantified using image-processing techniques. The method of measuringink dot uniformity is provided below.

Optical Uniformity Measurement

The dot images are loaded to the ImageXpert Software, preferably usingthe statistical rules provided hereinabove. Each image is loaded in eachof the Red, Green and Blue channels. The channel selected for the imageprocessing is the channel exhibiting the highest visible details, whichinclude the dot contour and color variance within the dot area, and thesubstrate surface fibrous structure. For example, the Red channel istypically most suitable for a cyan dot, while the Green channel istypically most suitable for a magenta dot.

For each of the selected dots, a line profile (preferably 3 lineprofiles for each of the at least 10 most representative dots) ismeasured across the dot area, crossing through the center of the dot.Since the line profile is measured on a single channel, gray values(0-255, non color values) are measured. The line profiles are takenacross the center of the dot and cover only the inner two thirds of thedot diameter, to avoid edge effects. The standard for sampling frequencyis about 8 optical measurements along the line profile (8 measured grayvalues evenly spaced along each micrometer, or 125 nm+/−25 nm permeasurement along the line profile), which was the automatic frequencyof the ImageXpert Software, and which was found to be suitable androbust for the task at hand.

The standard deviation (STD) of each of the line profiles is computed,and multiple line-profile STDs for each type of printed image areaveraged into a single value.

FIGS. 14A-1 to 14F-2 provide images of ink splotches or dots obtainedusing various printing technologies, and optical uniformity profilestherefor. More specifically, FIGS. 14A-2 to 14C-2 provide ink dot imagesdisposed on uncoated paper, for the following printing technologies: HPDeskJet 9000 (FIG. 14A-2); Digital press: HP Indigo 7500 (FIG. 14B-2);and Offset: Ryobi 755 (FIG. 14C-2). Similarly, FIGS. 14D-2 to 14F-2provide ink dot images disposed on commodity coated paper, for thoseprinting technologies.

FIGS. 14A-1 to 14F-1 provide the (non-color) gray relative value as afunction of the position on the line passing through the center of theink dot image, for each of the ink dot images provided by FIGS. 14A-2 to14C-2 (on uncoated paper), and by FIGS. 14D-2 to 14F-2 (on coatedpaper), for those printing technologies.

FIGS. 14A-3 to 14-F3 provide the contour analysis of these dots onuncoated and coated substrates as obtained by the afore-mentionedprinting technology of the art. The contour profile are used for thecalculation of the convexity characteristics of the printed dots.

FIGS. 12A-3 to 12E-3, respectively, provide graphs plotting the(non-color) gray relative value as a function of the position on theline passing through the center of the ink dot image, for each of theink dot images provided by FIGS. 12A-3 to 12C-3 (on coated paper), andby 12D-3 to 12E-3 (on uncoated paper). A relatively flat linear profilefor a particular ink dot image indicates high optical uniformity alongthe line.

The results would appear to confirm that the ink dots disposed on theuncoated fibrous printing substrates exhibit poorer uniformity withrespect to the corresponding ink dots disposed on the coated fibrousprinting substrates.

Moreover, for uncoated substrates, the line profile of the inventive inkfilm produced by the inventive system and process had an average STD ofabout 4.7, which compares favorably to the STD achieved using the priorart technology (19). For coated substrates, the line profile of theinventive ink dot produced by the inventive system and process producedan STD of about 2 to 2.7, which compares favorably, though lessstrikingly so, to the STD achieved using the prior art technology (4).

When comparing between films or dots on coated papers, the average ofeach of the standard deviations (STD) of the dot profiles of the presentinvention was always below 3.5. More generally, the STD of the dotprofiles of the present invention is less than 3.2, less than 3.0, lessthan 2.9, or less than 2.8.

In comparing between films or dots on uncoated papers, the standarddeviation (STD) of the dot profiles of the present invention was alwaysbelow 6. More generally, the STD of the dot profiles of the presentinvention is less than 15, less than 12, less than 10, less than 8, lessthan 7, or less than 6.

Because, as noted above, ink images may contain an extremely largeplurality of individual or single ink dots (at least 20, at least 100,at least 1,000, at least 10,000, or at least 100,000), it may bemeaningful to statistically define the inventive ink dot constructionswherein at least 10%, at least 20%, or at least 30%, and in some cases,at least 50%, at least 70%, or at least 90%, of the inventive ink dots(or inventive single-drop ink dots), disposed on any uncoated or coated(or commodity-coated) fibrous substrate, exhibit the above-mentionedstandard deviations for uncoated papers and for commodity-coated papers.

Penetration

In the ink film constructions of the present invention, the ink dot mayessentially be laminated onto a top surface of the printing substrate.As described herein, the form of the dot may be determined or largelydetermined prior to the transfer operation, and the dot is transferredas an integral unit to the substrate. This integral unit may besubstantially devoid of solvent, such that there may be no penetrationof any kind of material from the blanket transfer member into, orbetween, substrate fibers. The continuous dot, which may largely containorganic polymeric resin and colorant, adheres to, or forms a laminatedlayer on, the top surface of the fibrous printing substrate.

Such continuous dots are typically produced by various inkjettingtechnologies, such as drop-on-demand and continuous jettingtechnologies.

Referring again to the drawings, FIGS. 16A and 16B provide schematiccross-sectional views of an inventive ink film construction 300 and aninkjet ink splotch or film construction 370 of the prior art,respectively. Referring now to FIG. 16B, inkjet ink film construction370 includes a single-drop ink splotch 305 adhering to, or laminated to,a plurality of substrate fibers 320 in a particular continuous area of afibrous printing substrate 350. Fibrous printing substrate 350 may be,by way of example, an uncoated paper such as bond, copy, or offsetpaper. Fibrous printing substrate 350 may also be one of variouscommodity coated fibrous printing substrates, such as a coated offsetpaper.

A portion of ink splotch 305 is disposed below the top surface ofsubstrate 350, between fibers 320. Various components of the ink,including a portion of the colorant, may penetrate the top surface alongwith the ink carrier solvent, to at least partially fill a volume 380disposed between fibers 320. As shown, a portion of the colorant maydiffuse or migrate underneath fibers 320, to a volume 390 disposedbeneath fibers 320. In some cases (not shown), some of the colorant maypermeate into the fibers.

By sharp contrast, inventive ink film construction 300, provided in FIG.16A, includes an integral continuous ink dot such as individual ink dot310, disposed on, and fixedly adhering (or laminated) to, a top surfaceof a plurality of substrate fibers 320, in a particular continuous areaof fibrous printing substrate 350. The adhesion or lamination may be,primarily or substantially, a physical bond. The adhesion or laminationmay have little, or substantially no, chemical bonding character or morespecifically, no ionic bonding character.

Ink dot 310 contains at least one colorant dispersed in an organicpolymeric resin. Within the particular continuous area of fibroussubstrate 350, there exists at least one direction (as shown by arrows360—several directions) perpendicular to the top surface of printingsubstrate 350. With respect to all the directions normal to this topsurface over all of the dot area, ink dot 310 is disposed entirely abovethe area. The volume 380 between fibers 320 and the volume 390underneath fibers 320 are devoid, or substantially devoid, of colorant,resin, and any and all components of the ink.

The extent of penetration of an ink into a printing substrate may bequantitatively determined using various analytical techniques, many ofwhich will be known to those of ordinary skill in the art. Variouscommercial analytical laboratories may perform such quantitativedetermination of the extent of penetration.

These analytical techniques include the use of various stainingtechniques such as osmium tetroxide staining (see Patrick Echlin,“Handbook of Sample Preparation for Scanning Electron Microscopy andX-Ray Microanalysis” (Springer Science+Business Media, LLC 2009, pp.140-143).

One alternative to staining techniques may be particularly suitable toinks containing metals such as copper. Time of Flight Secondary Ion MassSpectrometry (TOF-SIMS) was performed using a TOF-SIMS V Spectrometer[Ion-ToF (Munster, Germany)]. This apparatus provides elemental andmolecular information with regard to the uppermost layer of organic andinorganic surfaces, and also provides depth profiling and imaging havingdepth resolution on the nanometric scale, submicrometer lateralresolution and chemical sensitivity on the order of 1 ppm.

Translation of the raw data of the TOF-SIMS into concentration may beperformed by normalizing the signals obtained to the carbon (C+)concentration measured by X-ray Photoelectron Spectroscopy (XPS), in thesample. The XPS data was obtained using a Thermo VG Scientific SigmaProbe (England). Small area chemical analysis of solid surfaces withchemical bonding information was obtained by using a microfocused (from15 to 400 μm) monochromated x-ray source. Angle resolved information isobtained with and without tilting the sample. This enables depthprofiling with good depth resolution.

As a baseline, the atomic concentration of copper within a fibrous papersubstrate was measured, as a function of depth. The atomic concentrationof copper was found to be substantially zero at the surface, down to adepth of several micrometers. This procedure was repeated for twocyan-colored inkjet ink film constructions of the prior art, and for acyan-colored ink film construction of the present invention.

Measurements of the atomic concentration of copper [Cu] within the inkdot and within the fibrous paper substrate, as a function of theapproximate depth, within a first cyan-colored inkjet ink filmconstruction of the prior art, were performed as described above. Theinitial [Cu], measured near the top surface of the cyan-containing inkfilm construction, was approximately 0.8 atomic %. Within a depth ofabout 100 nm, [Cu] dropped steadily to about 0.1 atomic %. Over a depthrange of about 100 nm-1,000 nm, [Cu] dropped from about 0.1 atomic % toabout zero. Thus, it is evident that the inkjet ink pigment haspenetrated into the fibrous paper substrate, possibly attaining apenetration depth of at least 700 nm, at least 800 nm, or at least 900nm.

Additional measurements of the atomic concentration of copper within theink dot construction, as a function of the approximate depth, within asecond cyan-colored inkjet ink film construction of the prior art, ledto the following findings: the initial atomic concentration of copper[Cu] within the ink dot construction, measured near the top surface, wasapproximately 0.02 atomic %. This concentration was generally maintainedover a depth of about 3,000 nm. Over a depth range of about 3,000 nm toalmost 6,000 nm, [Cu] dropped very gradually to about 0.01 atomic %. Itwould appear that this prior-art construction has little or no ink filmon the surface of the substrate, and that penetration of the pigmentinto the substrate was pronounced (at least 5-6 micrometers).

In view of the fundamental nature of the inventive laminated filmtransfer technology, described hereinabove (particularly with regard toFIGS. 16A and 16B) and in view of atomic concentration of copper [Cu]measurements performed by the inventors on similar ink filmconstructions, it is would appear manifest that the ink films of theinventive constructions are substantially solely disposed on the surfaceof the substrate, and that pigment penetration into the substrate issubstantially negligible, both in terms of penetration depth and interms of the penetration quantity or fraction.

Film Height or Thickness

Instrumentally measured heights (H) or thicknesses of single-film inkdots or splotches were obtained using a measuring laser microscope(Olympus LEXT 3D, model OLS4000). The LEP specimens typically had aheight or thickness within a range of 900-1150 nm; the lithographicoffset specimens typically had a height or thickness within a range of750-1200 nm.

With regard to ink dots or films produced from jetted ink drops, we havefound that the maximum average supra-substrate thickness of the ink dotmay be calculated from the following equation:

T _(AVG(MAX)) =V _(DROP)/[A _(FILM) *R _(VOL)]  (I)

wherein:

-   T_(AVG(MAX)) is the maximum average supra-substrate thickness;-   V_(DROP) is the volume of the jetted drop, or a nominal or    characteristic volume of a jetted drop (e.g., a nominal volume    provided by the inkjet head manufacturer or supplier);-   A_(FILM) is the measured or calculated area of the ink dot; and-   R_(VOL) is a dimensionless ratio of the volume of the original ink    to the volume of the dried ink residue produced from that ink.

By way of example, an ink dot disposed on a plastic printing substratehas an area of 1075 square micrometers. The nominal size of the jetteddrop is 10.0±0.3 picoliters. R_(VOL) was determined experimentally: avessel containing 20.0 ml of the ink was heated at 130° C. until a dryresidue was obtained. The residue had a volume of 1.8 ml. Plugging intoEquation (I), T_(AVG(MAX))=10 picoliters/[1075 μm²*(20.0/1.8)]=837 nm.

For generally round ink dots, the area of the ink dot may be calculatedfrom the ink dot diameter. Moreover, it was found that the dimensionlessratio R_(VOL) is generally about 10 for a wide variety of inkjet inks.

While for inks that penetrate into the substrate, the actual averagethickness may be somewhat less than T_(AVG(MAX)), this calculation mayreliably serve as an upper bound for the average thickness. Moreover, inthe case of various plastic substrates, and in the case of variouspremium coated substrates, the maximum average supra-substrate thicknessmay substantially equal the average supra-substrate thickness. In thecase of various commodity-coated substrates, the maximum averagesupra-substrate thickness may approach the average supra-substratethickness, often within 100 nm, 200 nm, or 300 nm.

With regard to ink dots or films produced from jetted ink drops, it wasfound that the maximum average supra-substrate thickness of the ink dotmay be calculated from the following equation:

T _(AVG(MAX))=[V _(DROP)*ρ_(INK) *F _(nRESIDUE)]/[A_(FILM)*ρ_(FILM)]  (II)

wherein:ρ_(INK) is the specific gravity of the ink;F_(nRESIDUE) is the weight of the dried ink residue divided by theweight of the original ink; andρ_(FILM) is the specific gravity of the ink.

Typically, the ratio of ρ_(INK) to p_(FILM) is approximately 1, suchthat Equation (II) may be simplified to:

T _(AVG(MAX))=[V _(DROP) *F _(nRESIDUE)]/A _(FILM)  (III)

For a wide variety of aqueous ink jet inks, F_(nRESIDUE) roughly equalsthe weight fraction of solids in the ink jet ink.

Using the above-described Olympus LEXT 3D measuring laser microscope,the height of above the substrate surface was measured for various inkdot constructions.

Atomic Force Microscopy (AFM) is another, highly accurate measurementtechnique for measuring height and determining ink dot thickness on asubstrate. AFM measurements may be performed using commerciallyavailable apparatus, such as a Park Scientific Instruments ModelAutoprobe CP, Scanning Probe Microscopy equipped with Proscan version1.3 software (or later). The use of AFM is described in depth in theliterature, for example, by Renmei Xu, et al., “The Effect of Ink JetPapers Roughness on Print Gloss and Ink Film Thickness” [Department ofPaper Engineering, Chemical Engineering, and Imaging Center for Ink andPrintability, Western Michigan University (Kalamazoo, Mich.)].

With regard to the ink film constructions of the present invention, theinventors have found that the thickness of the dry ink film on thesubstrate may be adjusted by modifying the inkjet ink formulation. Toobtain a lower dot thickness, such modifying may entail at least one ofthe following:

-   -   reducing the resin to pigment ratio;    -   selecting a resin or resins enabling adequate film transfer,        even with a reduced resin to pigment ratio;    -   utilizing finer pigment particles;    -   reducing the absolute quantity of pigment.

To obtain thicker dots, at least one of the opposite modifications(e.g., increasing the resin to pigment ratio) may be made.

Such changes in the formulation may necessitate, or make advantageous,various modifications in the process operating conditions. The inventorshave found that lower resin to pigment ratios may require a relativelyhigh transfer temperature.

For a given inkjet ink formulation, an elevated transfer temperature mayreduce ink film thickness. Increased pressure of the pressure roller orcylinder toward the impression cylinder during the transfer of theresidue film to a substrate at the impression station may also reduceink film thickness. Also, ink film thickness may be reduced byincreasing the time of contact between the substrate and theintermediate transfer member, interchangeably termed herein an “imagetransfer member” and both abbreviated ITM.

All this notwithstanding, a practical minimum characteristic (i.e.,median) thickness or average thickness for ink films produced accordingto the present invention may be about 100 nm. More typically, such inkfilms are single-drop ink films having a dot thickness, average dotthickness, or height (of the top surface of the dot) with respect to thesubstrate of at least 125 nm, at least 150 nm, at least 175 nm, at least200 nm, at least 250 nm, at least 300 nm, at least 350 nm, at least 400nm, at least 450 nm, or at least 500 nm.

Using the above-provided film thickness guidelines, the inventors areable to obtain inventive film constructions having an average thicknessof at least 600 nm, at least 700 nm, at least 800 nm, at least 1,000 nm,at least 1,200 nm, or at least 1,500 nm. The characteristic thickness oraverage thickness of a single drop film (or an individual ink dot) maybe at most about 2,000 nm, at most 1,800 nm, at most 1,500 nm, at most1,200 nm, at most 1,000 nm, or at most 900 nm. More typically, thecharacteristic thickness or average thickness of a single drop film maybe at most 800 nm, at most 700 nm, at most 650 nm, at most 600 nm, atmost 500 nm, at most 450 nm, at most 400 nm, or at most 350 nm.

Using the film thickness guidelines delineated hereinabove, theinventors are able to obtain inventive film constructions in which acharacteristic thickness or average thickness of the ink film may bewithin a range of 100 nm, 125 nm or 150 nm up to 1,800 nm, 1,500 nm,1,200 nm, 1,000 nm, 800 nm, 700 nm, 600 nm, 550 nm, 500 nm, 450 nm, 400nm, or 350 nm. More typically, the characteristic thickness or averagethickness of the ink film may be within a range of 175 nm, 200 nm, 225nm or 250 nm up to 800 nm, 700 nm, 650 nm, 600 nm, 550 nm, 500 nm, 450nm, or 400 nm. Suitable optical density and optical uniformity may beobtained, using the system, process, and ink formulations of the presentinvention.

The thickness (H_(dot)) of single-drop ink film or individual ink dot(shown schematically as dot 310 in FIG. 16A) may be at most 1,800 nm, atmost 1,500 nm, at most 1,200 nm, at most 1,000 nm, or at most 800 nm,and more typically, at most 650 nm, at most 600 nm, at most 550 nm, atmost 500 nm, at most 450 nm, or at most 400 nm. The thickness (H_(dot))of single-drop ink dot 310 may be at least 50 nm, at least 100 nm, or atleast 125 nm, and more typically, at least 150 nm, at least 175 nm, atleast 200 nm, or at least 250 nm.

Aspect Ratio

The inventors have found that the diameter of an individual ink dot inthe ink film constructions of the present invention may be adjusted,inter alia, by selection of a suitable ink delivery system for applyingthe ink (e.g., jetting) onto the ITM, and by adjusting the inkformulation properties (e.g., surface tension) to the requirements ofthe particular ink head.

This ink film diameter, D_(dot), or the average dot diameter on thesubstrate surface, D_(dot average), may be at least 10 micrometers, atleast 15 μm, or at least 20 μm, and more typically, at least 30 μm, atleast 40 μm, at least 50 μm, at least 60 μm, or at least 75 μm. D_(dot)or D_(dot average) may be at most 300 micrometers, at most 250 μm, or atmost 200 μm, and more typically, at most 175 μm, at most 150 μm, at most120 μm, or at most 100 μm.

Generally D_(dot) or D_(dot average) may be in the range of 10-300micrometers, 10-250 μm, 15-250 μm, 15-200 μm, 15-150 μm, 15-120 μm, or15-100 μm. More typically, with the currently used ink formulations, anda particular ink head, D_(dot) or D_(dot average) may be in the range of20-120 μm, 20-120 μm, 20-100 μm, 20-80 μm, 20-60 μm, 20-50 μm, or 25-50μm.

Each single-drop ink film or individual ink dot is characterized by adimensionless aspect ratio defined by:

R _(aspect) =D _(dot) /H _(dot)

wherein R_(aspect) is the aspect ratio; D_(dot) is the longest diameterof the dot; and H_(dot) is the average height of the top surface of dotwith respect to the substrate.

The aspect ratio may be at least 15, at least 20, at least 25, or atleast 30, and more typically, at least 40, at least 50, at least 60, atleast 75. In many cases, the aspect ratio may be at least at least 95,at least 110, or at least 120. The aspect ratio is typically below 200or below 175.

Surface Roughness

Using laser microscopy imaging and other techniques, the inventors haveobserved that the top surface of the ink dots in the ink filmconstructions of the present invention may be characterized by a lowsurface roughness, particularly when the substrates of thoseconstructions have a high paper (or substrate) gloss.

Without wishing to be limited by theory, the inventors believe that therelative flatness or smoothness of the ink film constructions of thepresent invention may largely be attributed to the smoothness of therelease layer on the surface of the ITM, and to the inventive system andprocess in which the emerging ink film surface substantially complementsthat of that surface layer, and in which the developing ink film imagemay substantially retain or completely retain that complementarytopography through the transfer onto the printing substrate.

Referring now to FIG. 17A, FIG. 17A is an image of the surface of arelease layer of an ITM or blanket used in accordance with the presentinvention. While the surface may be nominally flat, various pockmarks(recesses) and protuberances, typically of the order of 1-5 μm, may beobserved. Many of these marks have sharp, irregular features. An imageof an ink dot surface produced using this blanket, provided in FIG. 17B,displays topographical features that are strikingly similar in nature tothose shown in FIG. 17A. The dot surface is peppered with a largeplurality of marks having sharp, irregular features, which stronglyresemble (and are within the same size range as) the irregular marks inthe blanket surface.

A smoother blanket was installed; FIG. 17C provides an image of therelease layer of this blanket. The irregular pockmarks of FIG. 17A areconspicuously absent. Dispersed on the highly smooth surface are highlycircular surface blemishes, perhaps made by air bubbles, typicallyhaving a diameter of about 1-2 μm. An image of an ink dot surfaceproduced using this blanket, provided in FIG. 17D, displaystopographical features that are strikingly similar in nature to thoseshown in FIG. 17C. This image has virtually no distinctive pockmarks,but has a number of highly circular surface blemishes that arestrikingly similar in size and form to those shown of the blanketsurface.

Plastic Substrates

In view of the afore-mentioned results as observed on various fibroussubstrates, and in view of the fundamental nature of the inventivetransfer technology, the ink dots of the present invention are expectedto exhibit superior optical and shape properties, including roundness,convexity, edge raggedness, and surface roughness, on plastic printingsubstrates as well.

The non-convexity, or deviation from convexity for ink dots printed on awide variety of plastic printing substrates, may typically be at most0.020, at most 0.018, at most 0.016, at most 0.014, at most 0.012, or atmost 0.010. At least some of the ink dots, can exhibit non-convexitiesof at most 0.008, at most 0.006, at most 0.005, at most 0.004, at most0.0035, at most 0.0030, at most 0.0025, or at most 0.0020. On somesubstrates (e.g., polyester and atactic polypropylene substrates),typical ink dots may exhibit non-convexities of at most 0.006, at most0.004, at most 0.0035, and even more typically, at most 0.0030, at most0.0025, or at most 0.0020.

On all plastic substrates, individual ink dots in the ink dotconstructions according to the present invention may exhibit a typicaldeviation from roundness of at most 0.8, at most 0.7, at most 0.6, atmost 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most0.20, at most 0.18, or at most 0.15. On various smooth plastics, such asatactic polypropylene and various polyesters, individual ink dots mayexhibit a typical deviation from roundness of at most 0.35, at most 0.3,at most 0.25, at most 0.20, at most 0.18, at most 0.15, at most 0.12, atmost 0.10, at most 0.08, at most 0.06, at most 0.05, at most 0.04, or atmost 0.035.

Glass Transition Temperature of the Resin

The inventors have found that in selecting resins, and combinations ofresins, for use within the formulations supporting the ink filmconstructions of the present invention, the softening temperature (orglass transition temperature for at least partially amorphous resins)may be a useful indicator of resin suitability. Specifically, the resinsused in the ink formulations (and disposed in the ink films of thepresent invention) may have a glass transition temperature (T_(g)) of atleast 42° C., at least 44° C., at least 46° C., at least 48° C., or atleast 50° C. However, such resins may be too soft, which may negativelyimpact the abrasion resistance of the printed image, and may also beassociated with stickiness and flowability of the image at near-ambienttemperatures (e.g., around 40° C.). More significantly, such resins maycause clogging of the inkjet print heads, particularly when the blanketis hot and delivers heat to the jetting units. Thus, more typically, theTg may be at least 52° C., at least 54° C., at least 56° C., at least58° C., at least 60° C., at least 65° C., at least 70° C., at least 75°C., at least 80° C., at least 85° C., at least 90° C., or at least 95°C. The glass transition temperature is typically at most 120° C., atmost 110° C., at most 105° C., or at most 100° C., and in some cases, atmost 95° C., at most 90° C., or at most 85° C.

More generally, from a process standpoint, the ink formulations disposedon the ITM, after becoming devoid or substantially devoid of water, anyco-solvent, and any other vaporizable material that would be vaporizedunder process conditions, e.g., pH adjusting agents, (producing “inksolids”, a “dried ink residue”, or the like), and/or the resins thereof,may have a T_(g) of at least 42° C., at least 44° C., at least 46° C.,at least 48° C., or at least 50° C.

In the event that multiple glass transition temperatures are observed,the term T_(g), as used herein, refers to at least one of: (i) the glasstransition temperature of the predominant resin, on a weight basis, and(ii) to the highest Tg of the plurality of resins.

Analysis of Ink Films on Printed Substrates

3 sheets of printed matter (based on B2, 750×530 mm) are subjected tothe following procedure: after 1 week, the sheets are cut into 3×3 cmpieces and introduced into 300 grams of a solution containing 1%2-amino-2-methyl-1-propanol dissolved in water, which is able tosufficiently dissolve ink images printed using various water-solubleinks. If, however, the solution remains colorless, the water isseparated off and an identical weight of a less polar solvent, ethanol,is introduced. Again, if the solution remains colorless, the solvent isseparated off, and an identical weight of a less polar solvent, methylethyl ketone, is introduced. The procedure continues with successfullyless polar solvents: ethyl acetate, toluene, and Isopar™ (syntheticmixture of isoparaffins). After 5 hours stirring at room temperaturewith the most appropriate solvent, the mixture is filtered through a 5micrometer filter. The filtrate or filtrates containing the dissolvedink is dried using a rotary evaporator. The residues are then dissolvedin 5 grams of DMSO (or one of the above-listed solvents) and dried in anoven at 110° C. for 12 hours to yield the “recovered residue”.

The thermo-rheological behavior of the recovered residue may then becharacterized (e.g., by performing a viscosity “sweep” as a function oftemperature, as described above) and compared with thethermo-rheological behavior of a dried sample of the original ink, whenavailable. The inventors have found this procedure to provide a strongcorrelation between the thermo-rheological behavior of the recoveredresidue and the thermo-rheological behavior of a dried sample of theoriginal ink. The inventors believe that this correlation may beattributed to both the increase in residence time and the use ofadditional solvents of varying polarity.

This procedure may advantageously be used to produce andthermo-rheologically characterize dry ink residues recovered fromprinted matter such as magazines and brochures.

One of ordinary skill in the art will readily appreciate that other,potentially superior, procedures may be used to de-ink a printedsubstrate and produce the recovered ink residue for rheological,thermo-rheological and/or chemical analysis.

Ink Formulations and Ink Film Compositions

Among other things, the present inkjet inks are aqueous inks, in thatthey contain water, usually at least 30 wt. % and more commonly around50 wt. % or more; optionally, one or more water-miscible co-solvents; atleast one colorant dispersed or at least partly dissolved in the waterand optional co-solvent; and an organic polymeric resin binder,dispersed or at least partly dissolved in the water and optionalco-solvent.

It will be appreciated that acrylic-based polymers may be negativelycharged at alkaline pH. Consequently, in some embodiments, the resinbinder has a negative charge at pH 8 or higher; in some embodiments theresin binder has a negative charge at pH 9 or higher. Furthermore, thesolubility or the dispersability of the resin binder in water may beaffected by pH. Thus in some embodiments, the formulation includes apH-raising compound, non-limiting examples of which include diethylamine, monoethanol amine, and 2-amino-2-methyl propanol. Such compounds,when included in the ink, are generally included in small amounts, e.g.,about 1 wt. % of the formulation and usually not more than about 2 wt. %of the formulation. In other embodiments, the ink formulations are notsupplemented by pH modifying agents.

The ink film of the inventive ink film construction contains at leastone colorant. The concentration of the at least one colorant within theink film may be at least 2%, at least 3%, at least 4%, at least 6%, atleast 8%, at least 10%, at least 15%, at least 20%, or at least 22%, byweight of the complete ink formulation. Typically, the concentration ofthe at least one colorant within the ink film is at most 40%, at most35%, at most 30%, or at most 25%.

More typically, the ink film may contain 2-30%, 3-25%, or 4-25% of theat least one colorant.

The particle size of the pigments may depend on the type of pigment andon the size reduction methods used in the preparation of the pigments.Generally, the d₅₀ of the pigment particles is expected to be within arange of 20 nm to 300 nm. Pigments of various particle sizes, utilizedto give different colors, may be used for the same print.

The ink film contains at least one resin or resin binder, typically anorganic polymeric resin. The concentration of the at least one resinwithin the ink film may be at least 10%, at least 15%, at least 20%, atleast 25%, at least 35%, at least 40%, at least 50%, at least 60%, atleast 70%, or at least 80%, by weight.

The total concentration of the colorant and the resin within the inkfilm may be at least 10%, at least 15%, at least 20%, at least 30%, orat least 40%, by weight. More typically, however, the totalconcentration of the colorant and the resin within the ink film may beat least 50%, at least 60%, at least 70%, at least 80%, or at least 85%.In many cases, the total concentration of the colorant and the resinwithin the ink film may be at least 90%, at least 95%, or at least 97%of the ink film weight.

Nominally, the resin dispersion may be, or include, a polyester(including co-polyester) or an acrylic styrene co-polymer (orco(ethylacrylate metacrylic acid) dispersion. The acrylic styreneco-polymer from the ink formulation ultimately remains in the ink filmadhering to the printing substrate.

In one embodiment, the ink film in the ink film constructions accordingto the present invention is devoid or substantially devoid of wax.Typically, the ink film according to the present invention contains lessthan 30% wax, less than 20% wax, less than 15% wax, less than 10% wax,less than 7% wax, less than 5% wax, less than 3% wax, less than 2% wax,or less than 1% wax.

In one embodiment, the ink film according to the present invention isdevoid or substantially devoid of oils such as mineral oils andvegetable oils (e.g., linseed oil and soybean oil), or various oils usedin offset ink formulations. Typically, the ink film according to thepresent invention contains at most 20%, at most 12%, at most 8%, at most5%, at most 3%, at most 1%, at most 0.5%, or at most 0.1%, by weight, ofone or more oils, cross-linked fatty acids, or fatty acid derivativesproduced upon air-drying.

In one embodiment, the ink film according to the present invention isdevoid or substantially devoid of one or more salts, including saltsused to coagulate or precipitate ink on a transfer member or on asubstrate (e.g., calcium chloride). Typically, the ink film according tothe present invention contains at most 8%, at most 5%, at most 4%, atmost 3%, at most 1%, at most 0.5%, at most 0.3%, or at most 0.1% of oneor more salts.

In one embodiment, the ink film according to the present invention isdevoid or substantially devoid of one or more photoinitiators.Typically, the ink film according to the present invention contains atmost 2%, at most 1%, at most 0.5%, at most 0.3%, at most 0.2%, or atmost 0.1% of one or more photoinitiators.

In one embodiment, the printing substrate of the inventive ink filmconstruction is devoid or substantially devoid of one or more solublesalts, including salts used for, or suitable for coagulating orprecipitating ink, or components thereof, on the substrate (e.g.,calcium chloride). In one embodiment, the printing substrate of theinventive ink film construction contains, per 1 m² of paper, at most 100mg of soluble salts, at most 50 mg of soluble salts, or at most 30 mg ofsoluble salts, and more typically, at most 20 mg of soluble salts, atmost 10 mg of soluble salts, at most 5 mg of soluble salts, or at most 2mg of soluble salts.

In one embodiment, the ink film and formulation are substantially freeof saccharides. Typically, the concentration of saccharides, by weight,within the inventive ink is at most 6%, at most 4%, at most 3%, at most1%, at most 0.5%, at most 0.3%, or at most 0.1%.

In one embodiment, the ink film according to the present invention isdevoid or substantially devoid of one or more priming agents (such as acoagulating agent or viscosity-building agent). Such priming agents maybe jetted onto the surface of the substrate, or otherwise applied, aswill be appreciated by those of ordinary skill in the art. The primingagents may be applied solely in the vicinity of the subsequently jetteddrops, or may be applied substantially on the entire printing surface ofthe substrate. Typically, the ink film according to the presentinvention contains at most 2%, at most 1%, at most 0.5%, at most 0.3%,at most 0.2%, or at most 0.1% of such priming agents.

It will be appreciated that such a priming agent may chemically interactwith the printing substrate, or, more commonly, with a component of anink jet ink, to produce a “bonded priming agent”. Thus, in oneembodiment, the ink film according to the present invention is devoid orsubstantially devoid of one or more bonded priming agents. Typically,the ink film according to the present invention contains at most 2%, atmost 1%, at most 0.5%, at most 0.3%, at most 0.2%, or at most 0.1% ofsuch priming agents.

In one embodiment, the ink film in the ink film constructions accordingto the present invention contains at most 5%, at most 3%, at most 2%, atmost 1%, or at most 0.5%, by weight, of inorganic filler particles suchas silica.

In one embodiment, the dried resins present in the ink film of theinvention may have a solubility of at least 3%, at least 5%, or at least10% in water, at at least one particular temperature within atemperature range of 20° C. to 60° C., at a pH within a range of 7.5 to10 or within a range of 8 to 11. In alternative embodiments, thepolymeric resin is not highly soluble in water (e.g., less than 3%, byweight, at at least one pH within a range of 7.5 to 10), but dispersibletherein.

In one embodiment, the recovered ink film of the invention may have asolubility of at least 3%, at least 5%, or at least 10% in water, at atleast one particular temperature within a temperature range of 20° C. to60° C., at a pH within a range of 8 to 10 or within a range of 8 to 11.

Waterfastness of Print Images

ASTM Standard F2292-03 (2008), “Standard Practice for Determining theWaterfastness of Images Produced by Ink Jet Printers Utilizing FourDifferent Test Methods—Drip, Spray, Submersion and Rub”, may be used toassess the waterfastness of ink dots and films printed on varioussubstrates. The waterfastness of ink constructions according to thepresent invention can be evaluated by three of these test methods: drip,spray, and submersion.

In all three tests, several inventive ink film constructions exhibitedcomplete waterfastness; no ink bleeding, smearing or transfer wasobserved.

In some embodiments, the upper film surface contains at least one ofPEI, a poly quaternium cationic guar, such as a guarhydroxypropyltrimonium chloride, and a hydroxypropyl guarhydroxypropyltrimonium chloride.

In some embodiments, the upper film surface contains a polymer havingquaternary amine groups, such as an HCl salt of various primary amines.

As used herein in the specification and in the claims section thatfollows, the term “dye” refers to at least one colored substance that issoluble or goes into solution during the application process and impartscolor by selective absorption of light.

As used herein in the specification and in the claims section thatfollows, the term “average particle size”, or “d₅₀”, with reference tothe particle size of pigments, refers to an average particle size, byvolume, as determined by a laser diffraction particle size analyzer(e.g., Mastersizer™ 2000 of Malvern Instruments, England) or by adynamic light scattering particle size analyzer (e.g., Zetasizer™Nano-S, ZEN1600, also of Malvern Instruments, England), using standardpractice.

As used herein in the specification and in the claims section thatfollows, the term “geometric projection” refers to an imaginarygeometric construct that is projected onto a printed face of a printingsubstrate.

As used herein in the specification and in the claims section thatfollows, the term “distinct ink dot” refers to any ink dot or ink dotimage, at least partially disposed within the “geometric projection”,that is neither a “satellite”, nor an overlapping dot or dot image.

As used herein in the specification and in the claims section thatfollows, the term “mean deviation”, with respect to the roundness,convexity, and the like, of a plurality of “distinct ink dots”, refersto the sum of the individual distinct ink dot deviations divided by thenumber of individual distinct ink dots.

As used herein in the specification and in the claims section thatfollows, the term “weight” or “weight ratio”, with respect to a resin ina formulation or dried ink residue, is meant to include the entire resincontent within that formulation or residue, including, by way ofexample, the resin “binder” and any resin dispersant.

As used herein in the specification and in the claims section thatfollows, the term “softening agent” is used as the term would normallybe understood by those of skill in the art of polymeric resins. Thus, byway of example, a material added to a particular polymeric resin in aratio of 1:1 by weight, and attained insignificant softening of theresin (e.g., the Tg was lowered by less than 1° C.), would not beconsidered a “softening agent” with respect to that particular polymericresin.

With regard to fibrous printing substrates, persons skilled in theprinting arts will appreciate that coated papers used for printing maybe generally classified, functionally and/or chemically, into twogroups, coated papers designed for use with non-inkjet printing methods(e.g., offset printing) and coated papers designed specifically for usewith inkjet printing methods employing aqueous inks. As is known in theart, the former type of coated papers utilize mineral fillers not onlyto replace some of the paper fibers in order to reduce costs, but toimpart specific properties to paper, such as improved printability,brightness, opacity, and smoothness. In paper coating, minerals are usedas white pigments to conceal the fiber, thereby improving brightness,whiteness, opacity, and smoothness. Minerals commonly used to this endare kaolin, calcined clay, ground calcium carbonate, precipitatedcalcium carbonate, talc, gypsum, alumina, satin white, blanc fixe, zincsulfide, zinc oxide, and plastic pigment (polystyrene).

Coated papers designed for use in non-inkjet printing methods havehitherto been unsuitable for use with aqueous inkjet inks, or produceprint dots or splotches that may be manifestly different from theprinted ink film constructions of the present invention.

In contrast, specialty coated papers designed for use with inkjet inks,which in some cases may have layer of filler pigment as with other typesof coated papers, may also include a layer of highly porous mineral,usually silica, in combination with a water-soluble polymer such aspolyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP), which acts as abinder, upon which the ink is printed. Such coated inkjet papers aredesigned to quickly remove the water from the printed ink, facilitatingthe printing of ink droplets with good uniformity and edge roughness.The present invention encompasses ink droplets printed on uncoated paperas well as coated paper not designed for inkjet use, but someembodiments of the present invention are not intended to encompass inkdroplets printed on special coated inkjet paper.

Thus, in some embodiments, the substrate is an uncoated paper. In otherembodiments, the substrate is a coated paper that does not contain awater-soluble polymer binder in a layer upon which the ink is printed.

As used herein in the specification and in the claims section thatfollows, the term “commodity coated fibrous printing substrate” is meantto exclude specialty and high-end coated papers, including photographicpaper and coated inkjet papers.

In a typical paper coating of a commodity coated fibrous printingsubstrate, the coating formulation may be prepared by dispersingpigments, such as kaolin clay and calcium carbonate into water, thenadding in binder, such as polystyrene butadiene copolymer and/or anaqueous solution of cooked starch. Other paper coating ingredients, suchas rheological modifiers, biocides, lubricants, antifoaming compounds,crosslinkers, and pH adjusting additives may also be present in smallamounts in the coating.

Examples of pigments that can be used in coating formulations arekaolin, calcium carbonate (chalk), China clay, amorphous silica,silicates, barium sulfate, satin white, aluminum trihydrate, talcum,titanium dioxide and mixtures thereof. Examples of binders are starch,casein, soy protein, polyvinylacetate, styrene butadiene latex, acrylatelatex, vinylacrylic latex, and mixtures thereof. Other ingredients thatmay be present in the paper coating are, for example, dispersants suchas polyacrylates, lubricants such as stearic acid salts, preservatives,antifoam agents that can be either oil based, such as dispersed silicain hydrocarbon oil, or water-based such as hexalene glycol, pH adjustingagents such as sodium hydroxide, rheology modifiers such as sodiumalginates, carboxymethylcellulose, starch, protein, high viscosityhydroxyethylcellulose, and alkali-soluble lattices.

As used herein in the specification and in the claims section thatfollows, the term “fibrous printing substrate” of the present inventionis specifically meant to include:

-   -   Newsprint papers including standard newsprint, telephone        directory paper, machine-finished paper, and super-calendered        paper;    -   Coated mechanical papers including light-weight coated paper,        medium-weight coated paper, high-weight coated paper, machine        finished coated papers, film coated offset;    -   Woodfree uncoated papers including offset papers, lightweight        papers;    -   Woodfree coated papers including standard coated fine papers,        low coat weight papers, art papers;    -   Special fine papers including copy papers, digital printing        papers, continuous stationery;    -   Paperboards and Cartonboards; and    -   Containerboards.

As used herein in the specification and in the claims section thatfollows, the term “fibrous printing substrate” of the present inventionis specifically meant to include all five types of fibrous offsetsubstrates described in ISO 12647-2.

As used herein in the specification and in the claims section thatfollows, the term “dispersed”, with regard to a polymeric resin, ismeant to include a polymeric resin that is partially dissolved.

As used herein in the specification and in the claims section thatfollows, the term “jettable ink formulation”, and the like, refers to anink formulation that is suitable for repeated drop-on-demand jettingusing a drop-on-demand piezo print head.

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

It will be appreciated that certain features of the invention, whichare, for clarity, described in the context of separate embodiments, mayalso be provided in combination in a single embodiment. Conversely,various features of the invention, which are, for brevity, described inthe context of a single embodiment, may also be provided separately orin any suitable sub-combination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification, including PCT PublicationsNos. WO 2013/132418, WO 2013/132419, WO 2013/132420, WO 2013/132424, WO2013/136220, WO 2013/132339, WO 2013/132432 and WO 2013/132438, arehereby incorporated in their entirety by reference into thespecification, to the same extent as if each individual publication,patent or patent application was specifically and individually indicatedto be incorporated herein by reference. In addition, citation oridentification of any reference in this application shall not beconstrued as an admission that such reference is available as prior artto the present invention.

1-21. (canceled)
 22. A method of indirect printing comprising: a.providing a water-based ink formulation comprising: (i) a solventcontaining water; (ii) at least one colorant dispersed or at leastpartly dissolved within the solvent; (iii) at least one organicpolymeric resin, dispersed within the solvent; and (iv) a softeningagent selected to reduce a glass transition temperature (T_(g)) Of saidpolymeric resin, wherein the ink formulation provides all of a firstfeature, a second feature, a third features, a fourth feature, and afifth feature and feature, said first through fifth features beingdefined below; b. directing droplets of the ink formulation onto anintermediate transfer member (ITM) having a hydrophobic outer surface soas to form an ink image thereon; c. subjecting the ink image, on thehydrophobic outer surface of the ITM, to a heating-and-drying process soas to obtain an ink film; d. subjecting the ITM outer surface topressurized contact with substrate so as to transfer the ink filmthereto, wherein the first, second, third, fourth, and fifth featuresare defined as follows: i. according to the first feature, the inkformulation is either devoid of inorganic filler particles or has aninorganic filler particle concentration of less than 0.1 wt. %; ii.according to the second feature, the ink formulation forms, when dried,a substantially dry ink residue having: (A) a first dynamic viscositywithin a range of 10⁶ cP to 3·10⁸ cP over at least part of a firsttemperature range of 60° C. to 110° C.; and (B) a second dynamicviscosity of at least 6·10⁷ cP, over at least a part of a secondtemperature range of 50° C. to 55° C.; said second dynamic viscosity at55° C. exceeding the first dynamic viscosity at 85° C.; iii. accordingto the third feature, said softening agent has a pure vapor pressure ofat most 0.40 kPa at 150° C.; iv. according to the third feature, atleast one particular resin of said organic polymeric resin having anelevated glass transition temperature (T_(g)) of at least 54° C.; and v.according to the fifth feature, said softening agent is selected and/oradded in an amount to reduce said elevated glass transition temperatureby at least 5° C.
 23. The method of claim 22 wherein a thickness of theink film is at most 300 nm.
 24. The method of claim 22 wherein the inkformulation is devoid of inorganic filler particles.
 25. The method ofclaim 22 wherein the method is performed such that theheating-and-drying process renders the ink film tacky.
 26. The method ofclaim 22 wherein the method is performed such that immediately beforetransfer to substrate, the ink film is substantially dry.
 27. The methodof claim 22, wherein a weight ratio of said organic polymeric resin tosaid colorant is at least 3.5:1.
 28. The method of claim 27, whereinsaid weight ratio of said organic polymeric resin to said colorant is atleast 4:1.
 29. The method of claim 22, wherein said elevated glasstransition temperature (T_(g)) is at least 56° C.
 30. The method ofclaim 22, wherein said elevated glass transition temperature (T_(g)) isat least 60° C.
 31. The method of claim 22, wherein said softening agentis selected and/or added in an amount to reduce said elevated glasstransition temperature by at least 7° C.
 32. The method of claim 22,wherein said softening agent is selected and/or added in an amount toreduce said elevated glass transition temperature by at least 10° C. 33.The method of claim 22, wherein said softening agent is selected and/oradded in an amount to reduce said elevated glass transition temperatureby at least 15° C.
 34. The method of claim 22, wherein the formulationis an aqueous inkjet ink having at least one of: (i) a viscosity of 2 to25 cP at at least one particular temperature in a jetting temperaturerange of 20-60° C.; and (ii) a surface tension of at most 50milliNewton/m at at least one particular temperature within said jettingtemperature range.
 35. The method of claim 22, wherein ΔT defines atemperature differential between a temperature (T_(F)) at which saiddried ink residue begins to exhibit a particular degree of flowability,and a baseline temperature (T_(B)):ΔT=T _(F) −T _(B) said degree of flowability being defined by a criticalviscosity (μ_(CR)) at which said degree of flowability is achieved, andwherein, when said baseline temperature equals 50° C., and said criticalviscosity equals 10⁸ cP, said temperature differential is at least 3° C.36. The method of claim 22, said polymeric resin including, mainlyincluding, or consisting essentially of an acrylic-based polymerselected from the group consisting of an acrylic polymer and anacrylic-styrene copolymer.
 37. An ink film construction produced by themethod of claim 22, the ink film construction including: (a) theprinting substrate; and (b) the transferred ink film that wastransferred in step (d) of claim 22, the transferred ink substantiallydry and fixedly adhered to a surface of the printing substrate, thetransferred ink film containing at least one colorant dispersed in anorganic polymeric resin; wherein a dynamic viscosity of the transferredink film is within a range of 10⁶ cP to 5·10⁷ cP over at least part of afirst temperature range of 60° C. to 87.5° C., and at least 6·10⁷ cPover at least a part of a second temperature range of 50° C. to 55° C.,wherein a weight ratio of said organic polymeric resin to said colorantin the transferred ink film is at least 3.5:1.
 38. The ink filmconstruction of claim 37, a viscosity of said substantially dry inkresidue monotonically increasing with temperature decreasing from 85° C.to 55° C.
 39. A system for indirect printing, the system comprising: a.a quantity of a water-based ink formulation comprising: (i) a solventcontaining water; (ii) at least one colorant dispersed or at leastpartly dissolved within the solvent; (iii) at least one organicpolymeric resin, dispersed within the solvent; and (iv) a softeningagent selected to reduce a glass transition temperature (T_(g)) Of saidpolymeric resin, wherein the ink formulation provides all of a firstfeature, a second feature, a third features, a fourth feature, and afifth feature and feature, said first through fifth features beingdefined below; b. an intermediate transfer member (ITM) having ahydrophobic outer surface; c. an image-forming station at which dropletsof said ink formulation are directed onto said hydrophobic outer surfaceof said ITM so as to form an ink image thereon, wherein the system isconfigured to subject the ink image, on the hydrophobic outer surface ofthe ITM, to a heating-and-drying process so as to obtain an ink film,and wherein the system further comprises: d. an impression station atwhich the the ITM outer surface is subjected to pressurized contact withsubstrate so as to transfer the ink film thereto, and wherein the first,second, third, fourth, and fifth features are defined as follows: i.according to the first feature, the ink formulation is either devoid ofinorganic filler particles or has an inorganic filler particleconcentration of less than 0.1 wt. %; ii. according to the secondfeature, the ink formulation forms, when dried, a substantially dry inkresidue having: (A) a first dynamic viscosity within a range of 10⁶ cPto 3·10⁸ cP over at least part of a first temperature range of 60° C. to110° C.; and (B) a second dynamic viscosity of at least 6·10⁷ cP, overat least a part of a second temperature range of 50° C. to 55° C.; saidsecond dynamic viscosity at 55° C. exceeding the first dynamic viscosityat 85° C.; iii. according to the third feature, said softening agent hasa pure vapor pressure of at most 0.40 kPa at 150° C.; iv. according tothe third feature, at least one particular resin of said organicpolymeric resin having an elevated glass transition temperature (T_(g))of at least 54° C.; and v. according to the fifth feature, saidsoftening agent is selected and/or added in an amount to reduce saidelevated glass transition temperature by at least 5° C.
 40. The systemof claim 39, configured such that a thickness of the ink film which istransferred to substrate is at most 300 nm.
 41. The system of claim 39wherein the ink formulation is devoid of inorganic filler particles.